Council of Europe
In June 2025, Ukraine and the Council of Europe established a landmark Special Tribunal to prosecute senior Russian leaders for the crime of aggression, addressing a significant lacuna in existing international accountability mechanisms. This analysis critically examines the Tribunal’s legal foundations, jurisdictional parameters, and the substantial challenges confronting its operation, whilst evaluating its broader implications for the development of international criminal law.
Legal Context and the Imperative for a Special Tribunal
The Russian Federation’s full-scale invasion of Ukraine in February 2022 constituted an unequivocal violation of the UN Charter’s prohibition on the use of force, specifically Article 2(4), prompting widespread international condemnation and calls for accountability. Whilst the International Criminal Court (ICC) has initiated investigations into war crimes and crimes against humanity perpetrated in Ukraine, its jurisdiction over the crime of aggression remains constrained. The Court cannot prosecute aggression in this instance because the Russian Federation has neither ratified the Rome Statute nor accepted the Kampala amendments requisite for such jurisdiction. Furthermore, the institutional paralysis of the UN Security Council—attributable to Russia’s permanent member veto power—precludes the establishment of an ad hoc tribunal through traditional Chapter VII mechanisms.
This jurisdictional vacuum necessitated the exploration of alternative legal pathways. The Special Tribunal was conceived to prosecute specifically the crime of aggression, as defined under customary international law and codified in Article 8 bis of the Rome Statute: namely, the planning, preparation, initiation, or execution of acts of aggression that, by their character, gravity, and scale, constitute manifest violations of the UN Charter. The Tribunal’s establishment garnered robust support from European institutions and numerous states, reflecting a collective determination to ensure accountability for Russia’s highest-ranking officials.
Jurisdictional Scope and Institutional Architecture
The Tribunal’s jurisdiction has been deliberately circumscribed to prosecute the ‘leadership crime’ of aggression, focusing exclusively on individuals who bear the greatest responsibility for its commission, principally senior Russian political and military leaders. Significantly, the Tribunal’s jurisdictional remit extends to potential accomplices from third states, most notably Belarus, whose territory and resources facilitated Russian military operations against Ukraine.
The institutional framework represents an innovative departure from precedent. Established through a multilateral treaty between Ukraine and the Council of Europe, the Tribunal leverages the Council’s mandate to uphold human rights and the rule of law across the European continent. This novel structure diverges markedly from the traditional model of UN Security Council-established tribunals, such as the International Criminal Tribunal for the former Yugoslavia (ICTY) or the International Criminal Tribunal for Rwanda (ICTR). The Tribunal’s Statute incorporates procedural safeguards aligned with international fair trial standards and the European Convention on Human Rights, thereby seeking to secure broader international legitimacy and adherence to established human rights norms.
Principal Legal and Operational Challenges
Notwithstanding its innovative approach, the Tribunal faces legal and practical obstacles that may circumscribe its effectiveness.
1. The Doctrine of Immunity Ratione Personae
Perhaps the most significant legal impediment concerns the doctrine of immunity ratione personae, which traditionally shields incumbent heads of state, heads of government, and foreign ministers from prosecution in foreign jurisdictions (see here, and here). Whilst tribunals established under UN Security Council authority and the ICC possess explicit mandates to override such immunities, this Tribunal—created without UN imprimatur—must navigate these immunities more cautiously. The Tribunal’s Statute acknowledges immunities for serving heads of state, heads of government, and foreign ministers, effectively meaning that individuals such as President Putin would face prosecution only upon leaving office or in the unlikely event of immunity waiver by the Russian Federation. This limitation has attracted substantial criticism from legal scholars and practitioners (see here, here and here) who contend that it significantly undermines the Tribunal’s immediate deterrent effect and perpetuates a problematic precedent regarding impunity for the gravest international crimes.
2. Enforcement Mechanisms and Trials in Absentia
Related hurdles arise. The effectiveness of international arrest warrants depends upon suspects travelling to cooperating jurisdictions—a scenario of diminishing likelihood given heightened awareness of such risks amongst potential defendants. Without Russian co-operation and universal acceptance of any arrest warrants the Tribunal may issue, suspects may evade apprehension indefinitely, rendering the Tribunal’s jurisdiction largely symbolic.
Moreover, in the absence of Russian co-operation, defendants may need to be tried in absentia. That is possible under Article 28 of the Statute of the Special Tribunal, under stringent conditions—such as only doing so where the interests of justice require and where all reasonable steps have been taken to secure the defendant’s appearance. These limits are designed to protect defendants’ rights (Articles 16–20 of the Statute of the Special Tribunal). Such proceedings allow courts to try defendants who refuse to appear, though practical challenges persist in securing evidence, witness testimony, and ultimately executing judgments without the defendant’s state’s participation. Trials in absentia also such proceedings invariably risk perceptions of illegitimacy and may encounter resistance to international recognition of judgments rendered without the accused’s presence.
Accordingly, enforcement faces severe but not absolute barriers.
3. Selectivity and Questions of Political Legitimacy
The Tribunal faces inevitable accusations of selective justice—a critique that has long plagued international criminal law. Scholars have noted the absence of comparable accountability mechanisms for other alleged acts of aggression in recent history, such as the 2003 invasion of Iraq, arguing that the Tribunal’s establishment reinforces perceptions of geopolitical selectivity in international justice (see for example here, and here). Whilst proponents maintain that Ukraine’s case presents unique circumstances warranting exceptional measures, this criticism raises fundamental questions about consistency in international accountability. As a regional tribunal established under the Council of Europe’s framework, the Special Tribunal’s primary legitimacy derives from its European institutional foundation and the consent of participating states. However, the Tribunal’s effectiveness in setting precedents for international criminal law may depend on achieving broader acceptance beyond Europe, particularly given that the crime of aggression carries universal implications (see here, and here). The tension between regional authority and global impact presents a novel challenge: while the Tribunal need not secure universal endorsement to function within its jurisdictional framework, its contribution to developing international legal norms would benefit from wider recognition and political legitimacy, especially from states that have historically questioned the neutrality of international justice mechanisms.
Complementarity with Existing Accountability Mechanisms
The Tribunal’s relationship with existing judicial mechanisms has been carefully delineated to ensure complementarity rather than competition. In part, this is because the ICC does not have jurisdiction over the crime of aggression in Ukraine: Russia is not party to the ICC, and nor was Ukraine until this year; and while Ukraine accepted the jurisdiction of the ICC in 2015, the ICC’s jurisdiction in such situations (called referred jurisdiction) does not extend to the crime of aggression (Article 15bis(5), Rome Statute). Moreover, for other possible international crimes in Ukraine since Ukraine has ratified the Rome Statute, Article 1 of the Rome Statute acts as the principle of complementarity: the ICC is ‘complementary to national criminal jurisdictions’. Thus in practice, Ukraine has formally delegated jurisdiction over the crime of aggression to this international body, thereby avoiding jurisdictional conflicts with ongoing ICC investigations into war crimes, crimes against humanity, and genocide, or with domestic prosecutions under Ukrainian law. This architectural arrangement aims to maintain coherence across the spectrum of accountability processes, preventing duplication whilst ensuring comprehensive coverage of international crimes committed during the conflict.
Broader Implications for International Criminal Law
The Tribunal represents a watershed moment in the enforcement of international law’s prohibition against aggression. It offers opportunities to develop legal principles concerning state immunities and individual accountability for aggression, potentially crystallising contested doctrines in public international law. The Tribunal’s innovation lies in two converging features: establishment through a regional organisation without UN authorisation, and Ukraine’s exclusive delegation of jurisdiction over aggression crimes. Unlike previous tribunals operating under UN authority (ICTY, ICTR) or retaining concurrent domestic jurisdiction (hybrid courts), this model demonstrates how states can create binding international criminal mechanisms through regional frameworks when universal systems fail. The Council of Europe’s 46-member framework transforms what could have been a unilateral Ukrainian prosecution into multilateral justice, potentially establishing precedent for future tribunals when UN processes face obstruction.
However, enforcement remains a key challenge. While the Tribunal’s Statute establishes enforcement frameworks, practitioners must develop implementation strategies within these parameters, particularly for asset recovery, cross-border witness protection, and sentence enforcement agreements. These operational challenges require innovation within existing legal constraints. Third-state cooperation remains essential for arrests, evidence gathering, and asset freezing, particularly when defendants travel beyond Europe. Without wider support and acceptance of the Tribunal, enforcement remains geographically limited and potentially ineffective, as defendants could evade accountability through strategic travel to countries where an arrest warrant by the Tribunal does not bite. Thus, while regional authority provides a sufficient legal foundation, broader international acceptance enhances practical effectiveness and strengthens the Tribunal’s deterrent effect and legitimacy more broadly.
As with any international criminal institution (see here and here), the Tribunal faces heightened scrutiny regarding bias and politicisation. Operating outside UN frameworks intensifies these challenges, as opponents may dismiss regional tribunals as political instruments rather than impartial justice mechanisms. The Tribunal’s relationship with existing justice mechanisms presents specific challenges: preventing double jeopardy with ICC proceedings, coordinating evidence across institutions, resolving universal jurisdiction conflicts, and managing information sharing while respecting distinct mandates. Maintaining exceptional procedural standards and transparency becomes essential to counter such critiques and establish credibility as a model for future accountability efforts. Procedural challenges include ensuring effective legal representation for defendants tried in absentia, managing disclosure obligations without state cooperation, and maintaining judicial independence despite the political nature of aggression charges. These considerations will determine whether the Tribunal reinforces or undermines the international rule of law, potentially shaping future responses to acts of aggression in an increasingly fragmented global order. International law scholars and practitioners have an important role to play in evaluating the Tribunal in this regard.
Conclusion
The Special Tribunal for the Crime of Aggression against Ukraine represents both an ambitious innovation in international criminal law and a pragmatic response to extraordinary circumstances that have exposed lacunae in existing accountability mechanisms. The Tribunal’s unique institutional architecture and combination of regional authority and exclusive criminal jurisdiction for prosecuting aggression represents a departure from previous models of conflict-specific international criminal tribunals, which either operated under UN mandate or maintained concurrent domestic jurisdiction. Whilst confronting significant legal obstacles and practical limitations, its establishment signals a renewed commitment within the international community to ensuring accountability for leaders who perpetrate egregious breaches of international peace and security. The Tribunal’s ultimate impact upon the evolution of international law will depend upon careful navigation of legitimacy concerns, development of effective enforcement mechanisms within statutory constraints, and maintenance of procedural integrity.
Legal practitioners and scholars bear particular responsibility in addressing these challenges, ensuring that this institutionally novel Tribunal contributes to the progressive development of international criminal law whilst maintaining fidelity to fundamental principles of justice and due process. Scrutiny of procedural safeguards in particular, from pre-trial detention standards to appellate review mechanisms, will prove essential in establishing whether regional criminal tribunals can deliver justice that meets universal standards of fairness.
Bernardo Carvalho de Mello is a PhD student at Newcastle University Law School and holds a Masters in Constitutional Law from Pontifícia Universidade Católica do Rio de Janeiro. He is also a Global South Network representative.