On May 9, 2025, while Russia was commemorating the 80th anniversary of the Soviet Union’s victory over Nazi Germany, a coalition of States gathered in Lviv, in western Ukraine, announced the creation of a special international tribunal tasked with prosecuting the crime of aggression committed against Ukraine. This court, whose establishment is planned for 2026, will be mandated to prosecute senior Russian political and military leaders involved in the invasion of Ukrainian territory, which began on February 24, 2022.
The result of over two years of negotiations, this initiative brought together more than 40 States, including all European Union members except Hungary and Slovakia, as well as most G7 countries, with the exception of the United States. Based on an agreement concluded between Ukraine and the Council of Europe, but without a mandate from the United Nations and without any direct connection to the International Criminal Court (ICC), it represents a significant step forward in the international legal response to a large-scale war of aggression on European soil.
The creation of such an ad hoc jurisdiction is based on a principle reiterated by the European Union’s High Representative for Foreign Affairs, Kaja Kallas, who stated that “there is no space for impunity” in the face of such grave violations of international law. While the statute of the future tribunal has not yet been published, the main outlines of the project have been shared during several preparatory meetings. The special tribunal, established under the auspices of the Council of Europe and financed by participating States, will have jurisdiction to try top Russian political and military leaders not only for the invasion since 2022, but also for the annexation of Crimea in 2014. The aim is to remedy the current shortcomings of international criminal justice in prosecuting the crime of aggression.
Why create a new special international tribunal?
The crime of aggression, as defined in Article 8 bis of the Rome Statute – the ICC’s founding treaty –, consists in the planning or execution, by a political or military leader, of an act of aggression constituting a manifest violation of the United Nations Charter. It is one of the four crimes under the ICC’s jurisdiction, alongside genocide, crimes against humanity, and war crimes. However, due to its highly political and inter-State nature, and the fact that it only concerns individuals in a position to direct or control the political or military action of a State, its prosecution is subject to particularly restrictive jurisdictional conditions.
In the specific case of Ukraine – on which the ICC has been investigating since 2022 following a referral by several States Parties, prior to Ukraine’s accession in 2025 – current limitations prevent the Court from exercising jurisdiction over the crime of aggression, unlike other core international crimes. This legal gap in the current architecture of international criminal justice is precisely what the initiative for a special tribunal seeks to address.
Indeed, the ICC’s jurisdiction over the crime of aggression is highly dependent on the mode of referral. When the Court is seized by the UN Security Council (Article 15 ter of the Rome Statute), it may exercise jurisdiction unconditionally, even over non-State Parties. Nevertheless, this path is politically unfeasible in Ukraine’s case, given Russia’s veto power as a permanent member of the Security Council. Conversely, when the Court is seized by a State Party or the Prosecutor acting proprio motu (Article 15 bis), its jurisdiction is strictly conditioned: both the aggressor State and the victim State must be parties to the Rome Statute and must have ratified the 2010 Kampala Amendments without an opt-out declaration. Russia, however, is not a party to the Rome Statute and has not accepted the Court’s jurisdiction over the crime of aggression.
It is precisely the impasse in which the ICC finds itself with regard to the crime of aggression that justifies the initiative to create a special tribunal. As the Council of Europe has emphasized, such an ad hoc jurisdiction would fill this structural gap in international criminal law and bypass the political paralysis at the Security Council.
Nonetheless, the special tribunal will not operate in competition with the ICC, but in complementarity with it. In this regard, the ICC has already initiated several proceedings concerning the situation in Ukraine and has issued international arrest warrants, including against President Vladimir Putin, for the war crime of unlawful deportation of population (children) and unlawful transfer of population (children).
The special tribunal, for its part, will focus exclusively on the crime of aggression, targeting individuals in positions enabling them to direct or control the political or military actions of the State, starting with the members of the so-called “troika”: the Head of State, the Minister of Defence, and senior military officials. Leaders from other countries allied with Russia, such as Belarus or North Korea, could also be prosecuted if it is established that they actively participated in the crime of aggression.
Towards a trial of Vladimir Putin for the crime of aggression?
Russian President Vladimir Putin is, unsurprisingly, among the principal figures targeted by the initiative to create a special tribunal for the crimes of aggression against Ukraine. A central question remains, however: that of the immunity of sitting heads of State. Under customary international law, personal immunity (or ratione personae immunity) bars any prosecution against a head of State while in office. This rule was recalled by the International Court of Justice in its judgment on the Arrest Warrant of 11 April 2000 (Democratic Republic of Congo v. Belgium) (2000), confirming the inviolability of the highest representatives of the State abroad, including in the context of criminal proceedings.
As a result, Vladimir Putin could only be tried if he ceased to hold office, personally renounced his immunity, or if Russia itself waived it, scenarios that remain uncertain at this stage. Nevertheless, the special tribunal could anticipate such an eventuality by opening investigations, collecting evidence, and drafting a conditional indictment, all steps that would enable swift judicial action should circumstances become favourable.
Furthermore, the possibility of trials in absentia is being considered in cases where the accused refuses to appear or where all reasonable efforts to secure their presence have failed. Although controversial in international law due to concerns about upholding the rights of the defence, and to date only applied by the Special Tribunal for Lebanon, the Council of Europe suggests that this mechanism could be justified when the interests of justice so require, provided that fair trial guarantees are fully respected.
Finally, the special tribunal is expected to be equipped with cooperation mechanisms with States responsible for executing its decisions, including arrest warrants. Through this institutional framework, the aim is to realize the ambition expressed by the Council of Europe: to affirm that “war must not be waged as a tool of state policy” and that acts of military aggression must not go unpunished.
