Revue Européenne du Droit
Pursuing Accountability for the Crime of Aggression Against Ukraine
Issue #5


Issue #5


Federica D’Alessandra

Legal Journal published by the Groupe d’études géopolitiques in partnership with Le Club des juristes

A little over one year ago, multilateralism seemingly ‘lied on its deathbed’ 1 as the world’s second largest nuclear power, Russia, invaded neighbouring Ukraine right as the UN Security Council was meeting in New York in an eleventh-hour effort to ‘give peace a chance’. 2 For months, a massive military build-up by Russian forces at the border with Ukraine had raised concerns of an imminent and unprovoked invasion, to the Kremlin’s full-throated denial. About one hour into the meeting, however, from Moscow, President Vladimir Putin announced the start of his ‘special military operation’ 3 —or his naked aggression against Ukraine, as the rest of the world would see it. For weeks, the world watched in horror and dismay as Russian missiles rained on Ukrainian cities, indiscriminately targeting civilians and civilian infrastructure across the country, as far west as Lviv on the border with Poland, a NATO member; while Russian infantry and armoured divisions marched in from neighbouring Belarus and the embattled Donbass region towards the Ukrainian capital, in an attempt to overthrow the elected government of President Volodymyr Zelensky. 

The shock to the multilateral system was such that, well-beyond Europe, the invasion drew immediate and widespread condemnation, with only few notable exceptions. 4 Within days from the full-scale invasion, 141 countries at the UN voted in favour of a General Assembly resolution condemning Russia’s aggression against Ukraine, suspending Russia from the UN Human Rights Council, and demanding its unconditional withdrawal—but to no avail. 5 As a 60 km-long Russian military convoy reached the outskirts of Kyiv, many expected the capital to fall within days. The United States even offered President Zelensky evacuation, but he refused ‘the ride’, asking for ‘ammunition’ instead. 6 In the ensuing month-long Battle of Kyiv, to the surprise of most, the Ukrainian Armed Forces successfully halted the Russian offensive, forcing their first of many retreats. As Ukrainians took up arms and joined the resistance, Ukraine’s partners rallied around the invaded nation—a fierce ‘David on the Dnipro’ 7 — paying the ultimate price to defend its sovereignty, territorial integrity, and right to self-determination. 

One year later, Russian forces have lost 54% of their initial territorial gains, but remain hunkered down in the Southern and Eastern parts of Ukraine. 8 From their indiscriminate shelling across the country to the deployment of the ruthless Wagner mercenaries, from the sieges of Mariupol and Bakhmut to the countless, spineless acts of sexual violence, the trafficking of children, or the horrific massacres in cities such as Bucha, 9 the brutality of their tactics is revealed daily in the systematic trail of death and destruction they leave behind wherever they retreat. As shocking evidence of the unspeakable atrocities they have committed continues to mount, compounding the sense of outrage already felt at the illegal invasion, Ukraine and its partners in the international community demand accountability, putting international law front and centre in all debates. 

The Centrality of International Law in Ukraine’s Response to the Invasion 

It is a remarkable statement to the value of international law to those it is intended to protect that, even as it continues to defend itself militarily, Ukraine has chosen to simultaneously pursue any and all opportunities for legal remedy it has available against Russia and its leadership. Ukraine’s reliance on a variety of international law mechanisms as part and parcel of its response to Russia’s invasion can be understood as having various dimensions. In the context of a war being fought to prevent Ukraine’s alignment with European values and transatlantic institutions, the choice to mobilize the international rule of law in response to the invasion is immensely powerful at the symbolic level, for it contrasts Ukraine as a law-abiding nation to the ‘lawlessness’ of the invader. Equally, by deferring to international judicial processes and institutions wherever they are available, Ukraine can successfully demonstrate that it is pursuing every and all means it has available to resolve its dispute with Russia by peaceful means. This is meaningful especially in light of the fact that, as the victim of aggression, Ukraine is not required to do so under international law, for it has an undisputed right to defend itself militarily; however, by choosing to do so, Ukraine is indirectly demonstrating that Russia could have, in fact, done so itself, and that the recourse to war to settle its dispute with Ukraine was by no means of last resort, thus adding to the case for Russia’s responsibility for internationally wrongful acts. 

The choice is also meaningful at a strategic level: by engaging international law and global institutions as part of its quest for a just resolution of the war, Ukraine is helping the case internationally that the war is not just a European matter, but one of global concern. Most importantly, however, turning to international laws and institutions is key as an immediate instrument of protection and redress, both during and after the war: as the war continues to rage, Ukraine is turning to international judicial bodies to establish the empirical truth about what is taking place, both as a way to counter Moscow’s attempts to advance false narratives to justify the invasion, and to lay the foundation for fact-based assessments of culpability for the myriad of violations affecting both Ukrainian citizens and the Ukrainian State. These, it is hoped, will be key to supporting judicial accountability processes moving forward, as well as reparations and a just settlement once the war ends. 

Only days after the invasion begun, for example, Ukraine ‘sued’ the Russian State for violations of the UN Genocide Convention and other key human rights treaties before the UN International Court of Justice, in an attempt to get the international judicial body to finally and officially rebuke (part of) Russia’s casus belli, which it had already deployed in Crimea: that is a baseless claim that Ukraine was committing ‘genocide’ against ethnic Russians in its Eastern oblasts, ‘forcing’ Russia into a ‘humanitarian intervention’. 10 Using the Uniting for Peace Resolution to circumvent Russia’s veto on the Security Council, Ukraine asked the General Assembly to make a determination that Russia’s conduct amounts to international aggression, 11 and that Ukraine is entitled to war reparations 12 and justice for all victims of the war. 13  Pursuant to the same objective, in May 2023, the Council of Europe (CoE) created a register of damage for Ukraine as the first step towards an international compensation mechanism for victims of Russian aggression. 14

At Ukraine’s request, the UN, the EU and the OSCE have all dispatched investigative teams focusing on upholding both State and criminal liability for violations of the laws of war, committed by all parties. 15 Ukrainian authorities are also investigating and preparing to prosecute domestically over 70,000 such incidents. 16 And, benefitting of protections and remedy enshrined in the Rome Statute of the International Criminal Court (ICC)—to which neither Russia nor Ukraine are States Parties, but whose jurisdiction Ukraine has accepted dating back to 2013—Ukraine asked the ICC to intervene, in a move later backed by 43 ICC member States, which also referred the situation for investigation collectively to the Court. 17 As a result, the ICC swiftly deployed investigators and opened a field office in Ukraine. 18 In an unprecedented move, in March 2023 the Court proceeded with issuing arrest warrants against Putin himself, and his Children’s Rights Commissioner Maria Lvova-Belova, for war crimes relating to the illegal deportation and forced adoption of children from Russian occupied territories in Eastern Ukraine. 19 The extraordinary warrant is the first ever issued against the sitting Head of State of a Permanent Member of the Security Council—which is not a party to the Court. 

A Gap in the International Justice Architecture 

Ukraine’s focus on pursuing legal avenues has re-energized many in the international community, particularly those who see the enforcement of fundamental rules of international law—such as protections enshrined in the Geneva Conventions, and the prohibition against aggression—as key to the restoration of global security. Ukraine’s US and European partners, in particular, see this as a historical juncture, potentially a ‘second Nuremberg moment’—in reference to the trials set up by the Allies at the end of World War II, which became foundational to the post-War global order. 20 A gaping hole exists, however, in today’s judicial accountability landscape: if a variety of domestic and international tribunals will sit in judgement over international crimes committed during the war, no court today can exercise jurisdiction on the war itself, or the ‘crime of aggression’ as it is known in international law. 

On this basis, the government of Ukraine has proposed the establishment of a special aggression tribunal. 21 Different models are currently being explored but many legal, policy, and political issues remain to be addressed. Challenges are particularly acute in light of the unique features of the crime of aggression in international law. Against this background, this essay may constitute a primer to some of the key issues arising in this debate. It will first contextualize the nature of the crime of aggression (ie why it is so controversial, and the jurisdictional challenges to which it gives rise), and will then proceed by discussing the key legal and policy questions with the most bearing on the proposed tribunal, as well as models under consideration. It will conclude with the author’s own views and recommendations on the way forward for accountability for the crime of aggression, both in and beyond Ukraine. 

What is the Crime of Aggression?

In international law, the large-scale use of force by a State against the territorial integrity and political independence of another State is known as ‘international aggression’. Today, its prohibition is enshrined in the UN Charter, and considered a peremptory norm of international law binding all States at all times, for it is rightly seen as the bedrock and foundation of international peace and security. In today’s world, force can be lawfully used by States only in self-defence, and pursuant to UN Security Council authorization under its Chapter VII powers to enforce, maintain, and restore international peace and security’. 22 In international law, any breach of the prohibition against the unlawful use of force may entail State responsibility for an internationally wrongful act; egregious violations of this prohibition may amount to international aggression; and, at least since Nuremberg, international aggression also gives rise to the criminal liability of the military and political leadership of the aggressor State for the ‘planning, preparation, initiation or waging’ of the war of aggression. 23 At the end of World War II, both Nazi and Japanese defendants were charged, convicted, and executed for ‘crimes against peace’, as aggression was then known, for this was considered to be the ‘supreme’ offense against the international community. 24 After the judgement, the criminality of aggression was also enshrined in the Nuremberg Principles, 25 and today the crime of aggression is defined in both international customary and treaty law, more precisely in provisions contained in the Rome Statute of the ICC,  which were informed by—but do not overlap entirely with—the customary law definition of the crime. 26

The crime of aggression has long been controversial among States, as aggression is by nature a State act and a leadership crime, for it can only be committed by those in a position to direct the action of a State to wage war against another State. 27 Through the years, much of the controversy was aimed at who exactly would meet this leadership requirement, and whether specific iterations of the use of force by States should, in fact, be captured by the definition of a crime of aggression, either because they did not raise to a threshold of gravity comparable to the unleashing of a full-scale war, or because States maintained these should be considered as falling under one of the existing ‘exceptions’ to the prohibition against the use of force—for example, military operations carried out in self-defence against non-state armed groups operating from the territory of another, non-consenting State, or ‘genuine’ humanitarian interventions carried out to protect civilians from mass atrocities, even where these might be unsanctioned by the UNSC. 28 However, and although it took twenty years of negotiations to achieve it, the Rome Statute’s provision defining the crime of aggression was ultimately approved unanimously by all States Parties to the Court; and also non-States Parties such as Russia, which had also participated in the negotiations, approved the definition of the crime for the purposes of the Statute. 29   

The ICC’s definition makes it clear that liability for the crime of aggression attaches only to those in a position to ‘effectively exercise control over or to direct the political or military action of a State’. 30 This, in contrast to the customary law standard, which was articulated by the Nuremberg Military Tribunal in the High Command case in reference not to: ‘a person’s rank or status, but his power to shape or influence the policy of his State’. 31 According to this latter standard, for example, private and industry actors—such as Russian oligarchs—could also be liable for the crime of aggression. 32 In addition, the Rome Statute introduces a ‘gravity threshold’ differentiating between an act of aggression (only giving rise to State responsibility) and a crime of aggression (impugning the penal liability of specific leaders) where the underlying act of aggression by its ‘character, gravity and scale, constitutes a manifest violation’ of the UN Charter. This was intended to align as much as possible the Rome Statute provisions with the core ‘essence’ of the customary law definition of the crime, which is that the unlawful use of force ought to be large scale enough to amount to a war to be criminal. 33 The ICC definition also lists a series of acts of aggression that, meeting the requisite gravity threshold, and where perpetrated against the territorial integrity or political independence of another State, will amount to a crime of aggression. Many of these have been committed by Russia against Ukraine, including, among others: an armed attack, invasion, military occupation or annexation by the use of force, as well as bombardments, blockades, or the sending of mercenaries and irregular armed bands into the territory of another State. 34 Importantly, the list of acts of aggression provided in the ICC definition also covers the ‘action of a State in allowing its territory […] to be used by […] [an]other State for perpetrating an act of aggression against a third State’, which is of relevance to Belarus. 

Does the International Criminal Court Have Jurisdiction Over Aggression in Ukraine?

The short answer is, unfortunately, no. Because of the nature of the crime of aggression (both a State act and leadership crime, with self-evident political implications), States insisted on a separate jurisdictional regime for this particular offense, which would be a lot more stringent than the ICC’s jurisdiction over war crimes, crimes against humanity, and genocide. Over the twenty years they spanned, negotiations around the conditions for the ICC exercise of jurisdiction over the crime of aggression were extremely fraught, and resulted in a regime that is so narrow to cast doubt as to whether the Court might, in fact, ever be able to prosecute anyone for this offense. 35 Explicitly, the ICC cannot exercise jurisdiction on the crime of aggression over non-States Parties to the Court or their nationals; 36 arguably, in fact, even if aggression is committed against a States Party, the ICC’s exercise of jurisdiction over aggression would require the consent of the aggressor State. 37 At the moment, the only way for the ICC to exercise jurisdiction on aggression over a non-State Party is through a UNSC referral, 38 which is however out of the question in this situation. 

Why Can’t We Simply Give the International Criminal Court Jurisdiction? 

In light of the current limitations of the ICC’s jurisdiction with respect to the crime of aggression, some have proposed that the Rome Statute should be amended, either to remove the clause that bars it from exercising jurisdiction over non-State parties 39 —which explicitly applies to the crime of aggression 40 —or to allow for referrals by the UN General Assembly. 41 After all, as the ICC Prosecutor put it during the last Assembly of State Parties in December 2022: ‘when we recognise that there is a gap in that [legal] architecture, […] we should try to address it through the Rome Statute […]. We don’t want dilution, we want consolidation.’ 42 And it is worthy of note that by issuing its very first arrest warrants to include President Vladimir Putin himself, the Court is sending a strong signal that it is both willing and able to go right at the top of the Russian State apparatus in order to fulfil its mandate to enforce accountability for the highest level, most responsible perpetrators of international crimes under its jurisdiction. Thus, without question, amending the Rome Statute is an objective all States supporting Ukraine’s proposal for a special tribunal should work towards, to ensure that the Court will be able to exercise its jurisdiction if and when a similar situation may arise in the future–and even better yet, to deter it. In fact, a mandatory review of the Rome Statute amendments on the crime of aggression will be coming up as soon as 2024, 43 and it is incumbent upon States to take lessons learned from Ukraine into account in those negotiations.

The fact remains however that, at present, the Court does not have jurisdiction over the crime of aggression itself, and that—at least at the current stage—amending the Rome Statute appears unfeasible, for it would require ratification of such amendments by 2/3 of ICC States Parties, followed by a 7/8 (or consensus) vote by its Assembly 44 —a very high bar that would likely entail protracted negotiations—and, if history is of guidance, possibly years if not decades before the amendments become operational. This, at a time when urgency is paramount. Perhaps even more importantly, it remains unclear—and, in fact, highly unlikely—that the long-standing policy posture of those States that made the ICC aggression regime weak to begin with has indeed changed since the Rome Statute was amended to include the offense in 2010, and even more so since its jurisdiction over the crime was activated in 2017 thanks to ratification of the amendments by 30 ICC member States. That number has since grown to 44, 45 but still falls short of the 82 that would be currently required under the Statute to be amended any further. Indeed, as Professor Reisinger Coracini recently put it: ‘if amending the Rome Statute were an available option, many of those [..] arguing for the establishment of a S[pecial] T[ribunal] [..] would do nothing short of embrac[ing] it’, continuing ‘the reason why many supporters of a [Special Tribunal] argue for a two-tiered approach [..] is their understanding that a quick fix of the Court’s jurisdictional regime is unrealistic’. 46

Who Does Have Jurisdiction Over Aggression in Ukraine? 

Russia and Belarus both have jurisdiction over their nationals, and their respective domestic criminal codes also criminalize aggression. 47 However, unless there is a significant change in leadership, it is unrealistic to expect either to exercise jurisdiction over the current situation, given that their top political and military echelon stands accused of the crime of aggression. Aggression is, by nature, a transboundary act, and as the victim State, Ukraine has the strongest jurisdictional claim, for the crime is being committed on its territory. 48 Aggression is explicitly criminalized in Ukraine’s domestic penal code, 49 and its domestic definition of the crime is not limited to leaders. In fact, Ukraine has already identified at least 623 Russians who might be prosecuted under its domestic definition of the crime, 50 and its domestic judicial system does have precedent for prosecuting and convicting both Russian and Ukrainian nationals on this basis, 51 but past proceedings have drawn some concerns among international observers. 52 Other States might also be able to claim jurisdiction over specific suspects, for example if they are dual nationals, and if their domestic criminal codes equally extend liability for aggression to the rank and file. 53 And States that have criminalized aggression domestically are considering whether they could rely on the principles of universal or protective jurisdiction in this case. 

Indeed, international law recognizes that certain crimes are so serious that the duty to prosecute them transcends all borders, and this is the basis of a number of universal jurisdiction laws implemented by various States to allow them to prosecute international crimes domestically, irrespective of where they take place. Lithuania, for example, has announced it is investigating Russia’s crime of aggression on this basis. 54 However, it is debatable whether universal jurisdiction actually exists for aggression. 55 Poland, too, has announced it is investigating Russia’s crime of aggression, but based on the protective jurisdiction principle, a rule of international law that allows a sovereign state to assert jurisdiction over a person whose conduct outside its boundaries threatens the State’s security or interferes with the operation of its government functions. However, observers disagree on whether protective jurisdiction can be exercised by States that are indirectly affected by the conduct in question. 56 In fact, on the basis of this principle, Ukraine would have the strongest claim to exercise this form of jurisdiction as the directly affected State. However, any such jurisdictional assertions would run into a significant obstacle with respect to certain Russian and Belorussian high-level officials who are protected by sovereign immunities. 

What Is the Issue with Immunities?

International law is fundamentally, though not exclusively, an inter-State affair, the conduct of which is anchored on the principle of sovereign equality. A corollary of this principle is that par inter parem no habet imperium—ie a sovereign State cannot exercise jurisdiction over another sovereign State. On this basis, various forms of immunities are awarded to representatives of the State to allow them to carry out their sovereign functions. In the context of our discussion, at least two levels of immunities arise: personal immunity, or immunity ratione personae, a status-based immunity applying to a small number of high-level State officials because of their office—specifically the Head of State, Head of Government and Minister of Foreign Affairs—and functional immunity, or immunity ratione materiae, that is a conduct-based immunity applying with respect to acts performed in an official capacity. Personal immunities apply for as long as the person is in office, for both private and official acts; whereas functional immunities protect a State official, both during and after their time in office, but only for official acts they carried out while in office. 57 On this basis, then, both Presidents Putin and Lukashenko, as well as Russian Prime Minister Mikhail Mishustin and Foreign Minister Lavrov are entitled to personal immunity for as long as they are in office, and any of their official acts while in office should also be covered by functional immunity before another State’s domestic courts. 58 However, in international law, two grounds for exception exist with respect to the application of these immunities that are worth discussing. 

According to the first, immunities ratione materiae cannot be invoked when the relevant act constitutes an international crime. Many authoritative legal scholars are proponents of this view, 59 and the question has been under study by the UN International Law Commission (ILC) since 2008. However, this exception is not firmly established in international law, at least with respect to aggression itself: indeed in its study, the ILC found a ‘discernible trend’—not a clear one—in State practice ‘towards limiting the applicability of immunity from jurisdiction ratione materiae’, but only ‘in regard to certain types of behaviour that constitute crimes under international law’. 60 However, many experts (including Members of the ILC themselves, 61 as well as external legal observers 62 ) disagree that this exception exists; and if it does, they disagree that it applies to aggression, which is generally not listed among the types of acts to which this exception would apply, 63 presumably because aggression is by nature a State act. And even if one takes the view that the exception does exist, and that it applies to aggression, this exception only covers functional immunities, and does not apply to personal immunities, at least according to the prevalent view. 64  

The second potential ground for exception, applicable to both immunities ratione personae and ratione materiae, concerns the argument that such immunities (which would be available jointly, or at least with respect to personal immunities in a domestic court) cannot be invoked if the person is to be judged by an international tribunal. This exception is more widely, though not universally, 65 accepted to be grounded in established international law, and has been upheld in the jurisprudence of various international courts, including the ICC. 66 Indeed, Article 27 of the Rome Statute makes it clear that ‘Immunities or special procedural rules which may attach to the official capacity of a person, whether under national or international law, shall not bar the Court from exercising its jurisdiction over such a person’. 67 At the same time, Article 98 of the Statute also requires that: ‘The Court may not proceed with a request for surrender or assistance which would require the requested State to act inconsistently with its obligations under international law with respect to the State or diplomatic immunity of a person or property of a third State’, and that it may ‘not proceed with a request for surrender which would require the requested State to act inconsistently with its obligations under international agreements pursuant to which the consent of a sending State is required to surrender a person of that State to the Court’—that is, unless it can first obtain the concerned State’s consent to waive immunity or to proceed with surrendering the suspect. 68  

It is on the basis of these seemingly conflicting provisions that some member States in the past have refused to surrender State officials wanted by the Court—more specifically, sitting Heads of State such as then Sudanese President Omar al Bashir (indicted on charges that include genocide) whom they maintained was protected by personal immunity—even though the ICC’s intervention had been mandated by the UNSC. 69 The issue is likely to be relitigated in light of the recent arrest warrant against Vladimir Putin, but thus far the ICC judges have rejected the claim and reiterated that the ICC does not recognize immunities as applicable to suspects wanted by the Court. 70 I anticipate that the same argument will prevail with respect to the Putin arrest warrant as well. In any case, however, as mentioned above, Article 15bis(5) of the Statute explicitly bars the Court from exercising jurisdiction over aggression when committed by the nationals of a State that is not a party to the Statute (such as Russia); 71 so, insofar as aggression at the ICC is concerned, immunities are not the biggest issue. 72  

Importantly, many remain critical of the position that immunities do not apply—in general—to international tribunals, maintaining that this is, in fact, not a blanket pronouncement, and that the extent to which this exception applies will depend on the characteristics of the international tribunal—ie how it is formed, in whose jurisdiction it is grounded, etc. This is principally because an international court can only be delegated by its members jurisdiction that they themselves possess. Meaning that, unless jurisdiction is already possessed by its members States at the domestic level, some take the more restrictive view that a court—even if created at the international level—may otherwise be able to exercise jurisdiction only with the affected State’s consent, or through UN Security Council action under its Chapter VII powers. 73 In the case of Russia’s aggression, as mentioned, the strongest jurisdictional claim outside of Russia and Belarus is on the basis of Ukraine’s reliance on the territorial or protective principles, and the proposed international tribunal would be anchored in Ukraine’s own jurisdiction. 

This is extremely important as it has been argued that, as the State victim of aggression, Ukraine might be entitled to override immunities by relying on other cardinal rules of international law, such as the rights to self-defence and to self-help, as well as other principles under the laws of war. 74 If Ukraine can use lethal force to defend itself, the argument goes, including by targeting the commander-in-chief of the adversary, it should also be able to recur to non-lethal measures to repel the aggression—for example, arresting and detaining the enemy command, which is allowed under the laws of war. Under Ukraine’s right to self-help, then, what would otherwise be an unlawful exercise of jurisdiction over Russia’s officials should be considered a lawful countermeasure in response to the aggressor State’s own breach of international law. 75  In my opinion, this argument does have merit. It is untested, however, making its reliance much safer in combination with other legal arguments, such as the second ground for exception identified above concerning the non-applicability of immunities before a tribunal of ‘international character’—specifically, one grounded on the jurisdiction of Ukraine as the directly affected victim state. 

Why Wouldn’t Ukraine Itself Exercise Jurisdiction?

Given it has jurisdiction over aggression and that it could override immunities based on self-help and self-defence, shouldn’t Ukraine itself prosecute Russian and Belorussian leaders for aggression? The answer is varied but, at a minimum, Ukraine’s status as a victim state could cast concerns over the legitimacy and especially impartiality of any proceedings it would administer alone against the top-level political leadership of its adversary for what is, ultimately, a crime with political implications—no matter the talent and integrity of its judicial appointees. Equally, if Ukraine’s jurisdiction might be the gateway to unlock the issue of immunities, an indictment issued by its domestic judicial system would, certainly, have far less repercussions (and, possibly, a weaker jurisdictional claim) than if the indictment were issued by an international judicial authority. In addition, if the tribunal were not only international but also drew from broad membership of States beyond Ukraine, this would immensely benefit the tribunal itself, as a legal duty to cooperate, enforce, and comply with its decisions—which would presumably be written into its Statute—would arise for each of its member-States, as opposed to only Ukraine. 

This could result in not only greater expertise, resources, and capacity being available to the tribunal, but at a practical level—based on just how broad its membership would be—it could have the effect to relegate any leader wanted by the court to live their life as a fugitive of the law in many countries, a pariah only able to travel within Russia and perhaps a handful of other States, least they may face the threat of arrest elsewhere. This is, precisely, one of the most immediate effects that—it is hoped—will follow the ICC arrest warrant against President Putin, impacting all 123 of its States Parties. As mentioned above, however, the most important argument for asking an international judicial body—rather than the domestic authorities of Ukraine—to prosecute the crime of aggression is that relying exclusively on the self-defence argument to wave immunities is risky, for the argument remains untested; it would be wiser to leverage it in combination with the argument concerning the inapplicability of immunities before a tribunal of ‘international’ character, further discussed below.

Pathways to the Creation of a Special Tribunal for Aggression

For a tribunal to be considered ‘international’ with respect to the inapplicability of sovereign immunities, two conditions would need to be met. 76 First, the tribunal must be established under international law, either through creation on the basis of a source of international law, such as a treaty, or on the basis of authority derived from a source of international law, such as through the decision by an organ of an international organization, which can be the UN or a regional organization such as the EU or the CoE, acting within the competencies given to that organ under the treaty establishing the organization. Secondly, the ‘nature of an international criminal court or tribunal must be such that, through its establishment and its institutional design, it is sufficiently detached from national jurisdictions’, 77 and that it sufficiently reflects the will of the international community as a whole to enforce crimes under customary international law. As discussed above, the customary international law status of the crime of aggression is uncontested, although many (myself included) take the view that for the cohesive development of international law, it would be imperative that the tribunal indeed adopt the Rome Statute definition of the crime. 78 Arguably, in fact, Ukraine can already prosecute any of the suspects it has identified that do not meet the Rome Statute’s leadership requirement; and it is large part for these latter suspects that the issue of immunities might arise. For this reason, the analysis in this section will chiefly be dedicated to the nature and potential modalities of the creation of the tribunal itself, which as mentioned however would be anchored in the jurisdiction of Ukraine as the victim state of aggression. So, how could such a tribunal be created?

1- Creation by Treaty at the Request of the UNGA  

With respect to the first condition, one of the ways in which a tribunal could be created would be by bilateral treaty or agreement—specifically one entered into between Ukraine and an international organization such as the UN, the EU, or the CoE, for example. In the case of the UN, the General Assembly has ‘residual responsibilities’ on international peace and security matters under the Charter, 79 which observers argue could be triggered pursuant to a vote through the Uniting for Peace mechanism to instruct the UN Secretary General to conclude an agreement between the UN and Ukraine to this effect. Precedent for the creation of a tribunal by means of a treaty between the UN and the affected State already exists, for example in the creation of the Extraordinary Chambers in the Courts of Cambodia (ECCC), or the Special Court for Sierra Leone (SCSL), among others. 80 Although it is important to underscore that both precedents were, in reality, ‘internationalized’ or hybrid tribunals (the definition of which is further discussed below), and relied on the interested States’ consent to prosecute individuals on whom they already had jurisdiction, chiefly as their own nationals, none of whom were still in office at the time prosecutions took place. The notable exception being former Liberian President Charles Taylor, who was indicted by the SCSL as a sitting Head of State but prosecuted after he had left office (meaning he was no longer entitled to personal immunity at the time his prosecution took place), 81 for crimes (war crimes and crimes against humanity) to which functional immunity does not apply, and pursuant to a UNSC resolution for his arrest. 82 This is important because, as just mentioned above, the prosecution of sitting Heads of State has a history of profound controversy in international law. 83 So, while nothing prevents the UNGA from recommending the creation of a tribunal by treaty, such tribunal would still have to rely on States’ cooperation, which has not always been forthcoming in the past. To be clear, however, this is not an argument against a tribunal’s creation, which I believe is necessary. 

Equally, the UNGA could recommend or endorse the creation of such a tribunal by a regional organization, such as the EU or the CoE. 84 Here too, there already is precedent for a regional tribunal with jurisdiction over the crime of aggression, by virtue of Article 28A(1)(14) of the Malabo Protocol extending the jurisdiction of the proposed African Court of Justice and Human Rights over this very offense. 85 In this latter case, however, the establishing treaty would have to be entered into between Ukraine and that organization directly, be it the EU or the CoE. We might refer to this option as the ‘General Assembly Model’, 86 for in either case the UNGA would back – and, in fact, recommend – the establishment of a tribunal by international treaty prior to its creation. This model would be preferrable if we keep in mind the simultaneous fulfilment of the second condition mentioned above, given that a UNGA resolution could be understood as ‘reflect[ing] the will of the international community as a whole’. Some States, however, might be weary of the precedent this might create, on the basis of the same political rationale that limited the ICC’s ability to exercise jurisdiction over the crime of aggression. But the key question with this proposal is a different one: whether there is, in fact, sufficient appetite even within the UNGA to pass such a resolution; 87 without the prospective votes, tabling a resolution might, in fact, undermine the prospects for a special tribunal, and perhaps even the case for accountability for the crime of aggression more generally, as it would send the signal that a large chunk of the international community opposed upholding justice in the face of one of the greatest examples of a crime of aggression since the birth of the UN. The implication might be that, if not in this case, then aggression will never be prosecuted.

2- Creation by Treaty Through a European Regional Organization

A second option would be to create the tribunal independently and regionally in Europe, through authority derived not under the UN Charter, but under one of the regional organizations’ founding instruments. This means that the EU and the CoE could also both establish such a tribunal themselves. More specifically, the EU could do so under the scope of its foreign and security policy, ‘where the powers of the Union are sufficiently broad and flexible to be adapted to the circumstances of a specific situation’; 88 for this, too, precedent already exists by virtue of the EU’s previous establishment of the Kosovo Specialist Chambers, set up by treaty between the EU and Kosovo as the interested State. With respect to the CoE, ‘matters relating to national defence do not fall within the scope’ of the organization, 89 whose purpose is rather ‘to achieve a greater unity between its members for the purpose of safeguarding and realising the ideals and principles which are their common heritage and facilitating their economic and social progress’. 90 However, experts have argued that if ‘seen under the prism of accountability for the commission of an international crime, the fight against impunity and the need to ensure full reparation for the damage caused by the crime’, the establishment of a tribunal would not be ultra vires even if created in such a manner. 91 In fact, the Parliamentary Assembly of the CoE has already called for the creation of an ‘ad hoc international criminal tribunal’, 92 while the Rapporteur of its Committee on Legal Affairs and Human Rights has called for the creation of said tribunal even ‘on the basis of a multilateral treaty’, presumably between Ukraine and CoE member States. 93 Equally, the European Parliament has already passed a resolution explicitly endorsing the need for the creation of a special tribunal, 94 with the European Commission also announcing the establishment of a Center for the Prosecution of the Crime of Aggression (ICPA), to be created in the Hague and supported by Eurojust, 95 which the EU could build up into a court. We might hereinafter refer to this option as the ‘Regional Model’, which differs from the previous one in that, process-wise, UNGA endorsement would not need to be sought a priori, as both the EU and the CoE are regional organizations independent of the UN. 

One objection could be made to the fully ‘Regional Model’, which is that—by definition—such a tribunal would reflect the will of the region, rather than that of the ‘international community as a whole’. This is particularly true if the tribunal were created directly by the 27 members of the EU, and perhaps less so if the tribunal were created by the CoE, whose 46 members are representative of a broader variety of legal traditions, as well as political and military alliances. 96 It is precisely for this reason that, although a UNGA resolution would not be a priori necessary in either case, its endorsement would, without a doubt, be politically beneficial, even if it came after the regional organization in question moved independently to create the court. And in fact, if the tribunal were constituted regionally, this might perhaps sway some votes in the UNGA, particularly those from States concerned with the financial burden such an institution might impose on them, or those who might prefer amending the Rome Statute if the idea is to set a precedent potentially at the global level. An additional observation is that, even if the tribunal were created fully regionally, if the treaty was open to universal accession (in addition to, or instead of, UNGA endorsement), this might also be helpful to meet the second criteria above. 97 Making the treaty open to universal accession could also be instrumental for the tribunal’s proper functioning, as none of the options currently on the table would, in fact, create a legal obligation to cooperate on non-Member States. A regional court would certainly have a raison d’être, for the strongest consequences of the aggression are being felt regionally within Europe. A regional formulation would also be key to reasserting European stability for it would send the strong signal that European countries and their partners in the region remain steadfast in their commitment to the rule of law and to accountability, and that no aggressive threats will ever again be tolerated against its regional security. That being said, if a UNGA resolution could in fact be obtained, whether a priori or ex-post facto, it would be equally important to reassert – at the political level – that the crime of aggression is indeed a threat to global peace and stability, irrespective of which region is most affected. In fact, a UNGA resolution could be sought to this effect, with the specification that—where regional mechanisms are able and willing to step in, as it is the case here— priority should be given to investing in regional solutions.

3- Creation by Limited Multilateral Treaty

The third option that has been suggested would be the creation of the said tribunal through a multilateral treaty between Ukraine and other ‘willing’ States (we shall call this the ‘Multilateral Treaty Model’). With respect to the ‘Multilateral Treaty Model’, the biggest issue arising would squarely be that of immunities (although, I believe, it would also raise legitimacy concerns). Proponents of this model often cite the International Military Tribunal (IMT) at Nuremberg as precedent for the inapplicability of immunities before even a tribunal set up by a handful of States. However, such a comparison is misguided because the IMT was established by the Allies pursuant to their authority as occupying powers, meaning that the Allied Control Council could lawfully wave immunities for Nazi officials because the Council was, in fact, itself the government of Germany. 98 In this case, at least at present, it is highly unlikely that the governments of Russia and Belarus would agree to wave immunities for their leaders; and, although, as mentioned, the argument could be made that immunities would still not apply on the basis of Ukraine’s rights to self-help and self-defence, it is questionable whether a tribunal built on the basis of a limited multilateral treaty would fulfil the second condition mentioned above, that is that it should ‘sufficiently reflect the will of the international community as a whole’. Importantly, accepting the premise that any small group of states can independently come together and create a tribunal before which Head of State immunities would not arise – and even more so doing this specifically for the crime of aggression – would create a worrisome precedent that, in my view, could very easily be politicized or misused in the future, thus detracting to perceptions around the seriousness of aggression as an internationally justiciable criminal offense.

4- An Internationalized Set of Chambers

A fourth option being discussed would be the creation of an internationalized set of chambers anchored in Ukraine’s domestic judicial system (following an ‘Internationalized’ or ‘Hybrid’ model). 99 Unlike options I-III above, I see this option as relating less to the modality and authority on the basis of which a tribunal would be created (ie. bilateral treaty between the UN and Ukraine, at UNGA request; independent, bilateral treaty between a European regional organization and Ukraine; and limited multilateral treaty), and more to the character and institutional set up of the tribunal itself, irrespective of how it is created. The choice here being between an-ICC like court – ie. an independent international organization (with supranational elements), 100 applying international law and staffed entirely of international judges, counsel and prosecutors – or a ‘hybrid’ or ‘internationalized’ tribunal, for which ample precedent also exists. 101 A hybrid/internationalized tribunal (also often referred to as ‘hybrid’ tribunal, with names such as High, Specialist, or Extraordinary Chambers) would be anchored in–but sufficiently detached from–Ukraine’s domestic system, for it would enforce international law (alone or in combination with Ukrainian domestic law), and also draw from the external expertise of international judges and prosecutors attached to or embedded within the court. It appears that some States are indeed pivoting towards this option, 102 particularly the G7, 103 and according to a recent poll conducted among Ukrainian citizens, this would be their preferred option as well. Interestingly, 93% of respondents polled also expressed a preference for the hybrid court to be given jurisdiction over other international crimes alongside the crime of aggression. 104 It is true that no domestic system, alone, could cope with the volume of international crimes prosecutions that Ukraine’s current investigations demand, reason why Ukraine’s international partners should without a doubt also invest in building up and supporting Ukraine’s domestic judicial system. In fact, one proposal out there is concerned, precisely, with setting up a hybrid set of chambers specifically for war crimes, crimes against humanity, and genocide, to complement the jurisdiction of both the ICC and the proposed aggression tribunal. 105  

But if the idea of the proposed tribunal is to fill an accountability gap, then the tribunal’s jurisdiction should be complementary to—not overlapping with—that of the ICC.

The Ukrainian government has, thus far, flatly rejected the idea of a hybrid court for aggression, and so have some experts, as well as smaller European nations within the ‘core group’ of states (which includes but is larger than the G7) pushing for the creation of a tribunal. Critics of the hybrid model prefer instead ‘a fully international tribunal’ created by the General Assembly. 106 The assumption here being that–if it even were politically realistic–the latter would be a legally superior option. It is important to underscore, however, that the tribunals that are regularly cited as precedent for the UNGA-backed ‘international’ court–such as the SCSL, or the ECCC–are, in fact, themselves hybrid / internationalized courts, with some degree of anchorage in the domestic system of the affected state for which it was created. By all means, if a tribunal could realistically be created via the UN rather than the EU or CoE, one might reasonably prefer that outcome, politically speaking. If a UN tribunal were not politically viable however (as it currently appears to be the case), critics should not be so quick to discount the possibility of creating what would essentially be the same form of tribunal, but established under proper regional authority by a European institution–at least in my view.

In any case, the key obstacle with this proposal is that, as of currently, it might not be viable under the Constitution of Ukraine, and particularly Article 125, according to which ‘the establishment of extraordinary and special courts shall not be permitted’. 107 And for as long as Ukraine remains under martial law and in a state of emergency, no amendments to its Constitution are permitted. 108 Some have pointed to the 2019 creation of the High Anti-Corruption Court of Ukraine as potential precedent, particularly in light of the fact that, in May 2022, the Verkhovna Rada—Ukraine’s Parliament—passed legislation expanding its jurisdiction to include issuing orders ‘to seize the property of particular individuals and legal entities associated with the ongoing military aggression by the Russian Federation against Ukraine’. 109  Others have raised that ‘Ukraine judicial experts have explained […] that this provision is intended to prohibit temporary courts created by executive authority’, but that ‘[t]he prohibition would not likely apply to an internationalized domestic court […] created through the legislative process’. 110 However, it is doubtful from my perspective the extent to which the High Anti-Corruption Court, which does not have international judges or prosecutors (but rather international ‘advisors’, precisely because the alternative is barred under Article 125) is, in fact, a viable precedent. 

If the apparent constitutional obstacle could be overcome, I see a hybrid set of chambers as be a very–if not the most–suitable option, provided that it had the backing of a competent supranational organization (whether the UN or a European regional institution), that it applied international law (and better yet the ICC substantive definition of the crime of aggression), and only if international judges and prosecutors – rather than simply ‘advisors’ – could be embedded within it. Such requirements would be key not only to the court’s internationalized character, which could be crucial to overcoming the immunities hurdle, but to its very legitimacy, in light of the concerns addressed above with respect to Ukraine carrying out high-level aggression prosecutions alone as the victim State. Once again, ideally, such court would be set up via bilateral treaty between the international authority creating the tribunal and Ukraine. Supporting States that are not member of the international organization in question – including the United States in the case of a European court – could still partake in supporting the effort directly or indirectly by either themselves joining the treaty, or as the US currently does, for example, with respect to the Kosovo Specialist Chambers. 111

Legitimacy, Enforcement, and Cooperation Matters

As mentioned, whichever option is pursued, the tribunal would benefit of as broad a membership base as possible—for legitimacy, legal (ie immunities), and enforcement reasons. On this latter point, it is crucial to reiterate that the tribunal will need to rely on its member States for enforcement and cooperation, as cooperation by non-member States could only be imposed under Chapter VII powers by the UN Security Council, which do not extend to the UNGA by virtue of the Uniting for Peace mechanism. Equally, it is important to underscore that, given the proven challenges of executing an arrest warrant against a sitting Head of State, the tribunal might either have to wait for President Putin’s fall from grace, or carry out his and Minister Lavrov’s trials in absentia. 112 However, such trials are highly controversial, for they may violate certain rights of the accused; although, under certain conditions, they are not precluded under international law. 113 And while some say said trials would have ‘negligible value and legitimacy’ against such high profile defendants, others maintain that ‘the symbolic nature of a judgment by an ad hoc tribunal—even in absentia—should not be underestimated’. 114  

Conversely, others have argued that, given the unlikely scenario of a Putin arrest while in office, and the fact the personal immunity would no longer apply if he is surrendered after he leaves office, the question of immunities is largely an academic one, and ‘the likelihood of personal immunity ever being an issue in an actual trial is effectively zero’. 115 Arguably, however, the tribunal in question might not need to proceed to the trial stage, whether or not in absentia, to have an impact, for—as it is hoped will be the case with the ICC arrest warrant against Putin—such a warrant might already carry sufficient stigma and entail strong enough consequences for any suspect’s ability to travel freely and carry out official duties. A pending arrest warrant could also become crucial to reset the terms of relations in the event of a post-Putin Russia. In fact, precisely on this basis, some also question the political wisdom of creating a tribunal for Russia’s aggression while the war continues to rage, with its outcomes being all but predetermined. 116 However, as it is the case with the Rome Statute, 117 legal mechanisms could be built into the tribunal’s charter to facilitate a peace process if and when conditions might so require. Indeed, the importance of adopting a long-term perspective cannot be overestimated: from Charles Taylor to Omar al Bashir, from Slobodan Milošević to Hissen Habré, history bears witness to the mantra that the ‘long arch of international justice’ eventually catches up even with once powerful and seemingly untouchable individuals. For this reason, it is imperative to set up the tribunal in a way that keeps as many options as possible open, and so that -if the question did arise- it would stand the highest chance of having the inapplicability of immunities confirmed by its judges. Importantly, as some observers have noted, whichever form its establishment will take, the tribunal should seek to forge a cooperative relationship with the ICC. 118 This is, at least in part, to support the cohesive development of both substantive and procedural law moving forward, given that many believe—as I do—that the ultimate lesson States should take away from this experience trying to prosecute Russia’s aggression is that the Rome Statute should be re-amended to address at least some of its greatest limitations in exercising jurisdiction over this offense. 

The Imperative of Accountability for Russia’s Aggression  

One year after Russia’s full-scale invasion begun, there can be no doubt of just how consequential the shockwaves of its aggression have been. As decried by the UN General Assembly, 119 the humanitarian consequences of the war have been horrific, with a human toll that has since reached near-epic proportions—with half a million casualties, of which at least 21,000 Ukrainian civilians, and 16 million between the internally displaced and cross-border refugees. 120 The conflict has challenged Europe’s most basic assumptions on regional peace and security, leading historically neutral countries such as Switzerland to send weapons to Ukraine, Finland and Sweden to seek NATO membership, and even Germany to turn a point in its defence and military posture. 121 Equally, the conflict has brought the spectre of nuclear confrontation back on the world stage, 122 disrupted the global economy, leading to energy and food crises, 123 and challenged the cardinal rules that have anchored the conduct of international affairs since the end of World War II. At a UN Security Council meeting on the eve of the invasion, Kenya’s UN envoy put it starkly as it rebuked Russia’s ‘irredentism and expansionism’, citing its own colonial past, and urging a ‘recovery from the embers of dead empires in a way that does not plunge us back into new forms of domination and oppression’. 124 What is worse, Russia’s aggression against Ukraine—which started with the 2014 illegal annexation of Crimea, and the fomenting of separatist armed rebellions in the Donbass region—appears to be part and parcel of a worrisome, repeated pattern of blatant disregard for international law dating back to—at least—its 2008 invasion of Georgia, and visible in its ‘Veto abuse’ at the UN, and the involvement of its armed forces and irregular mercenaries in brutal campaigns of indiscriminate violence against civilians well beyond Ukraine, in places such as Chechnya, Syria and Mali, for example. 125 It is for this reason that accountability has rightly become a key component of debates surrounding Russia’s unlawful war.

Of course, Russia’s aggression against Ukraine is not the first time that force is unlawfully used by States in egregious breach of the UN Charter. In the minds of many outside the Euro-Atlantic region, past instances of Western military adventurism, and frustrations with the lack of accountability for the consequences of devastating military campaigns—such as the 2003 illegal invasion of Iraq—remain raw, and weight heavily in the background of this discussion. Equally, the irony is not lost on many that some of the States taking the proposal for a special tribunal most seriously today are, in fact, the same States that sought to restrict as much as possible the subject-matter jurisdiction of the ICC on the issue. At the same time, however, in light of rising geopolitical tensions, and fears that other powerful States may themselves be considering using armed force against less-powerful neighbours in other regions, many do feel a certain sense of urgency to reinstate the cardinal prohibition against aggression, and the potentiality of criminal consequences for its violation. And if, to some, the response to the crisis in Ukraine has been further evidence of long-decried double-standards, 126 others see the current momentum generated by the war in Europe as an opportunity to reclaim the universal nature of certain core international rules, and the global character of the fight against impunity. 127  

The Way Forward on Accountability for the Crime of Aggression, In and Beyond Ukraine

There can be no doubt that this is a momentous time in world affairs, and that the consequences of any action we take—or refuse to take—today will be felt for generations to come. Each of the models discussed above present unique legal and policy challenges that are difficult, but not impossible, to navigate. By this point, the need to hold Russian leaders accountable for their naked crime of aggression against the sovereign nation of Ukraine should be beyond dispute. Indeed, in my view, I believe European governments and their partners can and should move forward with asserting regional competence and willingness to punish criminally this heinous offense against the region’s peace and stability. Of course, proponents of any tribunal formulation could continue to consider seeking a resolution by the UN General Assembly aimed to reiterate that the crime of aggression is a threat to all nations’ peace and stability. Alongside general endorsement for a tribunal’s creation, the UNGA resolution could also explicitly stipulate that preference should indeed be given to its establishment through regional institutions. This not only on account of the fact that the strongest consequences of the war are being felt in Europe, but perhaps also as a way to ‘win over’ the votes of those States that for policy, strategic, or financial concerns would oppose its creation through the United Nations. At the same time, for reasons discussed above, if such endorsement were not anticipated to be forthcoming a priori by the UNGA, this should not be seen as a bar to the creation of the special tribunal, for European regional organizations already themselves possess the right to establish such a court—and could, in fact, build on existing initiatives such as the recently announced Center for the Prosecution of the Crime of Aggression precisely to this effect. 

It is my opinion that a court created by treaty between Ukraine and a regional organization in Europe, which is sufficiently distinct from Ukraine’s domestic judicial system and that entails the full participation of international judges, counsel and prosecutors (alongside Ukrainians) would be the strongest and most viable option. From a legal perspective, the international/lized character of the court would be crucial both to its legitimacy, as well as with respect to the inapplicability of immunities  (particularly if the ICC judges were to uphold the Bashir precedent with respect to the arrest warrant now outstanding against President Putin). Equally, however, I believe this model would be preferable also from both a policy and strategic perspective, for it would set a precedent that is at once strong but also not easily abused or replicated with ease—doing so would, in fact, require the bona fide, genuine, and strong diplomatic backing of the entire region most affected by the crime of aggression in the future—something that would require real diplomatic legwork, and that would be hard to ‘manufacture’ spuriously.

Whichever model is pursued, it should be clearly stipulated that the creation of a special tribunal for aggression today ought to be understood as a one-time, emergency measure aimed at prosecuting one of the most heinous crimes of aggression since the birth of the UN, precisely as a way to restore the cardinal prohibition against aggression and, with it, the global rule of law. Then, it also ought to be clear that establishing a special tribunal to prosecute the crime of aggression against Ukraine is not—and should not be seen—as a long-term substitute or alternative to the ICC, with whom the tribunal should be required to cooperate. In fact, if the establishment of the tribunal is to mean something outside of Europe and of Ukraine, its creation must become the catalyst that finally brings States Parties to the Rome Statute back to the negotiating table to address the limitations imposed on the ICC’s exercise of jurisdiction on the offense. By virtue of its permanence and universalist ambition, an ICC with robust authority and jurisdiction over all international crimes—including the ‘supreme international crime’ that is aggression—might be the best—and, in fact only—way forward to reassert once and for all the central role that criminal accountability for egregious violations of international law should and will play as a key tenet of world affairs. 


  1. UN Security Council Report, ‘In Hindsight: Ukraine and the Tools of the UN’ (28 February 2022), <> accessed 7 March 2023.
  2. UN Press, ‘‘Give Peace a Chance,’ Secretary-General Urges Russian Federation at Security Council Meeting on Ukraine, Saying too Many People Have Died’ (23 February 2022) <> accessed 7 March 2023.
  3. The Kremlin, ‘Address by the President of the Russian Federation’ (Moscow, 24 February 2022) <> accessed 7 March 2023.
  4. UNGA Res ES-11/1 (18 March 2022) UN Doc A/RES/ES-11/1; Council of Europe Committee of Ministers, ‘Decision 2.3 Situation in Ukraine’ (Strasbourg, 24 February 2022) CM/Del/Dec(2022)1426bis/2.3; European External Action Service, ‘Russia’s Aggression Against Ukraine: Press Statement by the High Representative/Vice-President Josep Borrel’ (24 February 2022) Press Statement; OSCE, ‘Joint Statement by OSCE Chairman-in-Office Rau and Secretary General Schmid on Russia’s Launch of a Military Operation in Ukraine’ (Vienna, 24 February 2022) Press Release; NATO, ‘Statement by NATO Heads of State and Government on Russia’s Attack on Ukraine’ (Brussels, 25 February 2022) Press Release (2022) 061; African Union, ‘Statement from the Chair of the African Union, H.E President Macky Sall and Chairperson of the AU Commission H.E Moussa Faki Mahamat, on the Situation in Ukraine’ (Addis Ababa, 24 February 2022); ECOWAS Commission, ‘Communique on the War in Ukraine (Abuja,  27 February 2022) Press Release; Pacific Island Forum, ‘Remarks: Pacific Islands Forum Secretary General Puna-Statement on Ukraine’ (Suva, 28 February 2022); Organization of American States, ‘Statement from the OAS General Secretariat on the Russian Attack on Ukraine’ (Washington, D.C., 24 February 2022) Press Release, Doc E-008/22; CARICOM, ‘CARICOM Statement on the Situation in Ukraine’ (Georgetown, 24 February 2022); CARICOM, ‘Statement of the Conference of CARICOM Heads of Government on the War and Humanitarian Crisis in Ukraine’ (Georgetown, 3 March 2022); Nordic Council, ‘President of the Nordic Council Condemns Russia’s Attack on Ukraine’ (Copenhagen, 24 February 2022).
  5. UNGA Res ES-11/1.
  6. Sharon Braithwaite, ‘Zelensky Refuses US Offer to Evacuate, Saying ‘I Need Ammunition, Not a Ride’’ CNN (February 26, 2022,) CNN <> accessed 7 March 2023.
  7. Munich Security Conference, ‘David on the Dnipro: Ukraine’s Fight for Freedom’ (17 February 2023) <> accessed 7 March 2023.
  8. New York Times, ‘Maps: Tracking the Russian Invasion of Ukraine’ 25 January 2023 <> accessed 8 March 2023.
  9. UN Human Rights Council, ‘UN Commission has found an array of war crimes, violations of human rights and international humanitarian law have been committed in Ukraine’ < accessed> 8 March 2023.
  10. Allegations of Genocide Under the Convention on the Prevention and Punishment of the Crime of Genocide Case (Ukraine v Russian Federation) [2022] ICJ; Application of the International Convention for the Suppression of the Financing of Terrorism and of the International Convention on the Elimination of All Forms of Racial Discrimination (Ukraine v Russian Federation) [2017] ICJ; Sergiy Sydorenko, ‘European Human Rights Court Rules on Russian Responsibility in Eastern Ukraine’ Euractiv (Brussels, 3 February 2023 <> accessed 7 March 2023.
  11. UNGA Res ES-11/1.
  12. UNGA Res ES-11/L.6.
  13. UNGA Res ES-11/L.7.
  15. UNGA Res 40/1 (7 March 2022) UN Doc A/HRC/RES/94/1; Elana Sánchez Nicolás, ‘EU Will Support Investigation into War Crimes in Ukraine’ EUObserver (Brussels, 13 April 2022) <> accessed 7 March 2023; OSCE, ‘OSCE Special Monitoring Mission to Ukraine (Closed) <> accessed 7 March 2023.
  16. EuroNews, ‘Zelenskyy Says 70,000 War Crimes Committed in Ukraine as Kyiv moves to Open ICC Office’ (4 March 2023) <> accessed 7 March 2023.
  17. ICC, ‘Ukraine – Situation in Ukraine’ <> accessed 7 March 2023.
  20. Silvia Ellena, ‘Ukraine War Crimes ‘Another Nuremberg Moment,’ US Says’ Euractiv (24 May 2022) <> accessed 7 March 2023.
  21. Office of the President of Ukraine, ‘We must create a Special Tribunal on the crime of aggression against Ukraine’ <> accessed 7 March 2023.
  22. UN Charter, art 2, art 39, and Chapter VII.
  23. Yoram Dinstein, ‘The Crime of Aggression under Customary International Law’ in Leila Sadat (ed), Seeking Accountability for the Unlawful Use of Force (Cambridge University Press 2018), pp. 124-162.
  24. Judgement of the Nuremberg International Military Tribunal 1946 (1947) 41 AJIL 172.
  25. These were drawn up by the UN International Law Commission (ILC) at the request of the UN General Assembly, in an attempt to extrapolate general principles of international law arising from the tribunal and its judgement. See Principles of International Law Recognized in the Charter of the Nürenberg Tribunal and in the Judgment of the Tribunal (1950) <> accessed 7 March 2023.
  26. Carrie McDougall, The Crime of Aggression as Custom and the Mechanisms for Determining Acts of Aggression (Cambridge University Press 2017).
  27. Ibid. Also see: Rome Statute, art 8bis.
  28. Christian Wenaveser and Stefan Barriga, ‘18 Forks in the Road: Personal Reflection on the Kampala Amendments on the Crime of Aggression’ in Suzannah Linton, Gerry Simpson and William A Schabas (eds) For the Sake of Present and Future Generations (Brill 2015), pp. 281-297.
  29. ICC, Crime of Aggression <> ‘Understandings’ in Annex III of Resolution 6 of Kampala Review Conference.
  30. Rome Statute, art 8bis. Emphasis added.
  31. Emphasis added. United States v. von Leeb et al., Military Tribunal XII, 11 Trials of War Criminals Before the Nuernberg Military Tribunals Under Control Council Law No. 10 (1950), 489.
  32. IG Farben case, p 1124.
  33. The customary definition of the crime of aggression is thus narrower than that of the ICC; and although its precise contours are debated, various possible definitions under customary international law have been catalogued by scholars, including Claus Kress and Stefan Barriga, The Crime of Aggression: A Commentary (Cambridge University Press 2016).
  34. Rome Statute, art 8bis.
  35. Claus Kress, The Crime of Aggression (Cambridge University Press 2017); also see Kevin Jon Heller, ‘Creating a Special Tribunal for Aggression Against Ukraine is a Bad Idea’ Opinion Juris (7 March 2022) <> accessed 7 March 2023.
  36. Rome Statute, art 15bis(5).
  37. Rome Statute, art 15 (bis), paras 4-5.
  38. Rome Statute, art 15ter.
  39. Luis Moreno Ocampo, ‘Ending Selective Justice for the International Crime of Aggression’ Just Security (31 January 2023).
  40. Rome Statute, art 15bis(5).
  41. Jennifer Trahan, ‘The Need to Reexamine the Crime of Aggression’s Jurisdictional Regime’ Just Security (4 April 2022).
  42. ICC, ‘Statement by the ICC Prosecutor Mr. Karim A.A. Khan KC to the Assembly at the first plenary meeting’ (5 December 2022) <> accessed 8 March 2023.
  44. Rome Statute, art 121.
  47. Russian Penal Code, art 343; Belarus Penal Code, art 122.
  48. Cedric Ryngaert, ‘Public International Law Approaches to Jurisdiction’ in Jurisdiction in International Law (Oxford University Press 2008), pp. 21-41.
  49. Ukraine Penal Code, art 437.
  50. Sergey Vasiliev, ‘The Reckoning for War Crimes in Ukraine Has Begun’, Foreign Policy (17 June 2022).
  51. Specifically, two low-ranking Russian soldiers were convicted of violating Art. 437(2) by entering Ukraine and participating in hostilities in the Luhansk region, as well as the former President of Ukraine, Viktor Yanukovych, for complicity in conducting an aggressive war on the basis of the same provision for asking Putin to send Russian troops into Ukraine after he was removed from office.
  52. Sergey Sayapin, ‘A Curious Aggression Trial in Ukraine: Some Reflections on the Alexandrov and Yerofeyev Case’, Journal of International Criminal Justice 16 (2018), p. 1094; Sergey Sayapin, ‘The Yanukovych Trial in Ukraine: A Revival of the Crime of Aggression?’, Israel Yearbook on Human Rights 50 (2020), p. 65.
  53. For example, Ukraine’s penal code.
  54. Carrie McDougall, ‘Why Creating a Special Tribunal for Aggression Against Ukraine is the Best Available Option: A Reply to Kevin Jon Heller and Other Critics’ Opinio Juris (15 March 2022). Also see,
  55. Kevin Jon Heller, ‘Options for Prosecuting Russian Aggression Against Ukraine: A Critical Analysis’ Journal of Genocide Research (2022).
  56. For differing opinions, see McDougall (n 48), for ‘no’, and Heller (n 49) for ‘maybe’.
  57. Malcolm N. Shaw, ‘Immunities from Jurisdiction’ in Immunities in International Law (Cambridge University Press 2003), pp. 621-693.
  58. Arrest Warrant of 11 April 2000 (Democratic Republic of the Congo v Belgium [2002] ICJ Rep, para 61.
  59. Institute of International Law, Resolution on the Immunity from Jurisdiction of the State and of persons Who Act on behalf of the State in case of International Crimes, Napoli Session, 2009, art III, §1-2.
  60. ILC, ‘Report of the International Law Commission on the Work of its 69th Session’ (21 May-2 June and 3 July-4 August) UN Doc A/72/10, pp. 178-179, commentary to art 7, §5.
  61. Ibid.
  62. Advisory Committee on Public International Law, No. 40 Challenges in Prosecuting the Crime of Aggression: Jurisdiction and Immunities (2022).
  63. ILC, ‘Immunity of State Officials from Foreign Criminal Jurisdiction – Texts and Titles of the Draft Articles Adopted by the Drafting Committee on First Reading’ (31 May 2022) UN Doc A/CN.4/L.969, p. 2.
  64. Oliver Corden and Vaios Koutroulis, ‘Tribunal for the Crime of Aggression Against Ukraine – A Legal Assessment’ (European Parliament 2022). Finally, even if there is some support for a view that the exception to immunity for serious international crimes reflects existing international law and covers the crime of aggression, it should be noted that this does not seem to be shared by all EU Member States.
  65. Heller, ‘Creating a Special Tribunal for Aggression Against Ukraine is a Bad Idea’.
  66. The Prosecutor v Omar Hassan Ahmad Al-Bashir (Judgment) ICC-02/05-01/09 OA2 (6 May 2019), paras. 113-117;  Judgment in the Jordan Referral, paras. 113-117; Prosecutor v Charles Ghankay Taylor (Decision on Immunity from Jurisdiction) SCLS-2003-01-I, para. 52-53; Prosecutor v Milošević (Decision on Review of the Indictment and Application for Consequential Orders) ICTY-99-37-PT (24 May 1999).
  67. Rome Statute, Art 27.
  68. Rome Statute, Art 98.
  69. The Prosecutor v Omar Hassan Ahmad Al-Bashir, Judgment in the Jordan Referral, paras. 113-117.
  70. Ibid.
  71. Rome Statute, art 15bis5.
  72. Thus far, the only ICC member States that have been critical of the arrest warrant against Vladimir Putin, based on him being the sitting Head of State of a country that is not party to the Court have been Hungary and South Africa. Notably, South Africa, who is hosting the G20 in just a few months, was one of the countries which refused to surrender then President Omar al Bashir, whose transfer to the Court is still pending. For a rolling list of updates on which countries have spoken out against the ICC Putin arrest warrant, see:
  73. Dapo Akande and Talita de Souza Dias ‘Does the ICC Statute Remove Immunities of State Officials in National Proceedings? Some Observations from the Drafting History of Article 27(2) of the Rome Statute’ (14 November 2018) <> accessed 8 March 2023; Max Du Plessis and Dire Tladi ‘The ICC’s immunity debate – the need for finality’ EJIL:Talk! (11 August 2017) <> accessed 8 March 2023.
  74. Also see: Tom Dannenbaum, ‘Mechanisms for Criminal Prosecution of Russia’s Aggression Against Ukraine’ Just Security (10 March 2022); Dapo Akande, ‘A Criminal Tribunal For Aggression in Ukraine’ (at 41:20) Chatham House <> accessed 7 March 2023.
  75. Anton Moiseienko, ‘Russian Assets, Accountability for Ukraine, and a Plea for Short-Term Thinking’ EJIL:Talk! (5 March 2022) <> accessed 8 March 2023.
  76. Claus Kress, Commentary on Article 98 RS, para. 123 et seq.
  77. Astrid Reisinger Coracini and Jennifer Trahan, ‘The Case for Creating a Special Tribunal to Prosecute the Crime of Aggression Committed Against Ukraine (Part VI): On the Non-Applicability of Personal Immunities’ Just Security (8 November 2022).
  78. Ibid. Also see, for example, McDougall (n 48).
  79. UN Charter, art 11.
  80. David Scheffer, ‘Prosecuting the Crime of Aggression in Ukraine’ USIP (at 47:43) 7 December 2022.
  81. Prosecutor v Charles Ghankay Taylor (Decision on Immunity from Jurisdiction) SCLS-2003-01-I, para. 52-53.
  82. Helmut Kreicker, ‘Immunities,’ in Kress and Barriga (n 30), p. 683.
  83. The Prosecutor v Omar Hassan Ahmad Al-Bashir (Judgment) ICC-02/05-01/09 OA2 (6 May 2019), paras. 113-117;  Judgment in the Jordan Referral, paras. 113-117.
  84. James Goldstone and Anna Khalfaoui ‘In Evaluating Immunities before a Special Tribunal for Aggression Against Ukraine, the Type of Tribunal Matters’ Just Security (1 February 2023).
  85. Sergey Sayapin, ‘The Crime of Aggression in the African Court of Justice and Human and Peoples’ Rights’ in The African Court of Justice and Human and Peoples’ Rights in Context (CUP, 2019).
  86. Goldstone and Khalfaoui (n 70). In more detail, see Heller (n 49). Hereinafter, I adopt their same terminology in reference to the four models under discussion.
  87. For example, Kevin Jon Heller points out that ‘the African Union, which represents more than 50 states, categorically rejects the idea that personal immunity is inapplicable before international courts. It is thus almost inconceivable that more than a small number of African states would vote for such a resolution – even one that was limited to Russian aggression’; adding that ‘a significant number of states in the Middle East and Southeast Asia either voted against or abstained on Res. ES-11/1, which said nothing about a Special Tribunal or personal immunity but simply deemed Russia’s invasion of Ukraine an act of aggression. And an even greater number voted against or abstained on Res. ES-11/L.4, removing Russia from the Human Rights Council, including a significant group of states in South America’,
  88. Olivier Corten and Vaios Koutroulis, ‘Tribunal for the crime of aggression against Ukraine – a legal assessment’ European Parliament, December 2022, 19.
  89. Council of Europe, Statute of the Council of Europe, European Treaty Series – No. 1, 5.V.1949, London, 5 May 1949, art 1(d).
  90. Council of Europe, Statute of the Council of Europe, European Treaty Series – No. 1, 5.V.1949, London, 5 May 1949, art 1(a).
  91. Corten and Koutroulis (n 74) 18.
  92. Resolution 2436, adopted in April 2022.
  93. Aleksander Pociej, ‘The Russian Federation’s Aggression Against Ukraine: Ensuring Accountability for Serious Violations of International Humanitarian Law and Other International Crimes,’ Report of the Parliamentary Assembly of the Council of Europe, 26 April 2022, 15.
  94. European Parliament, Resolution on the establishment of a tribunal on the crime of aggression against Ukraine, (2022/3017(RSP) 18 January 2023.
  95. Eurojust, International Centre for the Prosecution of the Crime of Aggression made official at United for Justice Conference in Ukraine, Press Release, 5 March 2023.
  96. In fact, Kevin Jo Heller has observed that it might be more likely that CoE rather than EU member states are more amenable to constituting an aggression tribunal given that 80% of them have either criminalized aggression domestically, or ratified the Rome Statute’s amendment on aggression. He goes even further by suggesting that a Council of Europe-backed tribunal, which in his preference should be a hybrid set of chambers, ‘would also minimize the problem of unclean hands. Although the UK and France are members of the CoE, most of the other states responsible for limiting the ICC’s jurisdiction over aggression and/or for the invasion of Iraq – the US, Canada, Australia, New Zealand – are not’. However, in my view, according to this latter test, the EU would be an even better fit, given only France, among the States he lists, is a member. See: Heller (n 49).
  97. See, for example, Kress (n 62) para. 123 et seq.
  98. Janet Anderson, ‘Everything You Need to Know or Argue About a Special Tribunal on Russia’s Crime of Aggression’ Justice Info (13 December 2022).
  101. In fact, all precedents referenced above are examples of internationalized courts, differing however in terms of how they were set up. Such as the Special Court for Sierra Leone, or the Extraordinary Chambers in the Courts of Cambodia, for example. See David Scheffer (n 69).
  104. Also see this Memorandum signed by Ukrainian civil society and partner organizations
  105. In a more recent post, the same authors have also suggested that the model could also accommodate aggression prosecutions, for example for Parliamentarians and the Defense Minister, but admittedly not for the Russian President and Foreign Minister, given their personal immunity.
  107. Ukraine Constitution, art 125.
  108. ‘Legal jurists in Ukraine agree, however, that ‘if a court to try the crime of aggression is created not as a domestic court but as a wholly international one, then Article 125 of the Ukrainian Constitution is not a bar to establishing such a tribunal.’ In Alexander Komarov and Oona A Hathaway, ‘Ukraine’s Constitutional Constraints: How to Achieve Accountability for the Crime of Aggression’ Just Security (5 April 2022).
  109. Cameron McKenna and Nabarro Olswang, “Ukraine Expands Sanctions against Russia and its Supporters,” Lexology, 20 May 2022, cited in Heller(n 49).
  112. As it was stipulated, for example, in: United Nations Security Council, Resolution 1757 (2007) on the establishment of a Special Tribunal for Lebanon, UN Doc S/RES/1757 (2007), 30 May 2007, article 22.
  113. Sergey Vasiliev, ‘Aggression against Ukraine: Avenues for Accountability for Core Crimes’, EJIL:Talk! 3 March 2022.
  114. Corten and Koutroulis (n 74) 35.
  117. Art 16 and 53
  118. David Scheffer, ‘Forging a Cooperative Relationship Between International Criminal Court’ Just Security (25 October 2022).
  119. UNGA Res ES-11/2 (28 March 2022) UN Doc A/RES/ES-11/2.
  120. UN Human Rights Council, ‘Operational Data Portal – Ukraine Refugee Situation’ <> accessed 7 March 2023.
  121. Bundesregierung, ‘Policy Statement by Olaf Scholz, Chancellor of the Federal Republic of Germany and Member of the German Bundestag, 27 February 2022 in Berlin (Berlin, 27 February 2022) <> accessed 7 March 2023.
  122. Jon Stone, ‘Stop ‘Nuclear Sabre-Rattling,’ NATO Chief Tells Putin’ The Independent (Brussels, 23 March 2022) <> accessed 7 March 2023; Julia Mueller, ‘Put Puts US Officials on Edge with Nuclear Sabre-Rattling’ The Hill (Washington, D.C., 2 October 2022) <> accessed 7 March 2022.
  123. UN Sustainable Development Group, ‘Global Impact of War in Ukraine on Food, Energy and Finance Systems – Brief No. 1’ (April 2022) <> accessed 7 March 2023.
  124. NPR, ‘Kenyan U.N. ambassador compares Ukraine’s plight to colonial legacy in Africa’ 22 February 2022.
  125. UN, ‘Mali: Independent rights experts call for probe into Wagner Group’s alleged crimes’ (31 January 2023) <> accessed 8 March 2023.
  126.; Luis Moreno Ocampo, ‘Ending Selective Justice for the International Crime of Aggression’ Just Security (31 January 2023).
  127. James Goldston, ‘Ukraine and the Rebirth of Human Rights’ Project Syndicate (28 February 2023).
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