More than two years into Russia’s full-scale invasion of Ukraine, discussions continue regarding accountability mechanisms for the crime of aggression committed on Ukraine’s territory. One proposal posits the creation of a special tribunal based on a treaty between Ukraine and the Council of Europe (CoE) or its member States. 

Among the legal questions to consider with such a tribunal are the characteristics that would make it sufficiently “international” to overcome certain immunities that might otherwise apply to high-ranking Russian officials. To qualify as “international,” a tribunal must not be incorporated into the domestic legal system of Ukraine or any other State. In addition, to overcome the personal immunities, the tribunal must be acting on behalf of the “international community as a whole.”

The Proposal for a New Tribunal Between Ukraine and the Council of Europe

Discussions to create a new tribunal to prosecute Russian aggression against Ukraine have circulated since the full-scale invasion’s early days (creating a new tribunal is necessary because of the limitations in the International Criminal Court’s (ICC) exercise of its jurisdiction over the crime of aggression). Some proposals would establish a tribunal by treaty between the United Nations and the government of Ukraine, but other models have also emerged. A special tribunal based on a treaty between Ukraine and the CoE appears to be the latest option considered by the involved States.

In early April, the 44 States taking part in the Ministerial Conference on Restoring Justice for Ukraine adopted a political declaration  encouraging the interested States and international organizations “to secure a sound legal basis and broad international support” for the establishment of the special tribunal. In a press conference held on the same day, the European Commissioner for Justice Didier Reynders signaled that the option of “multilateral agreement or a bilateral agreement between the Council of Europe and Ukraine” was being discussed as a legal basis for the special tribunal (see here starting at 26:00). In May, the CoE Committee of Ministers tasked the CoE Secretary General with preparing “any necessary documents to contribute to the consultations within the Core Group” on a possible draft agreement between the CoE and Ukraine on the creation of the special tribunal and tribunal’s statute. 

The views among the involved States as well as the academic community as to the preferred form and nature – international or domestic – of such a tribunal vary (e.g. analyses by Tom Dannenbaum, Carrie McDougall, Kevin Jon Heller, and Owiso Owiso). One argument in favor of establishing an international rather than a domestic ad hoc tribunal is that the personal immunities of the acting State leaders, (the head of State, prime minister, and minister of foreign affairs – the “troika”), apply only before a domestic court but do not bar prosecution before an international criminal court (e.g. discussions by McDougall; Dannenbaum; Jennifer Trahan; Astrid Reisinger Coracini; Chile Eboe-Osuji). In such a case, two questions arise: under what conditions is a tribunal considered “international enough” to overcome these personal immunities? And, would the CoE-led option amount to such an international tribunal? 

The argument presented here is twofold. As a starting point, an international tribunal is any court that is both (1) not domestic, and (2) established either by at least two States or by an international organization and a State. However, that does not necessarily make a tribunal “international enough” to overcome personal immunities. Something more is required for a tribunal to be considered, in the words of the Special Court for Sierra Leone (SCSL), “truly international” (Decision on immunity from jurisdiction, para 38). 

International vs. Domestic Form

The term “international” means the opposite of domestic, i.e. relating to two or more nations. A tribunal need not be universal to be international. A regional or bilateral treaty or court, while not universal, is still international (Joint Concurring Opinion, para 57). There are three cumulative criteria for a criminal tribunal to be deemed international. 

First, the process of tribunal’s establishment must involve more than one State. This criterion is satisfied if the tribunal is established by two or more States, (e.g.,ICC which has 124 State parties), between a State and intergovernmental organization (e.g., SCSL), or by an intergovernmental organization (e.g., International Criminal Tribunal for the Former Yugoslavia (ICTY), International Criminal Tribunal for Rwanda (ICTR), and Special Tribunal for Lebanon (STL)). All of these configurations involve more than one State acting either directly or via an intergovernmental organization. 

Second, an international tribunal must be established based on international law, which in practice means that the tribunal is created on a treaty basis as is the case of the ICC and the SCSL. While the ICTY and ICTR were created by United Nations Security Council resolutions, the Security Council’s power to create such organs  derives from Chapter VII of the U.N. Charter, a treaty.

Third, the tribunal must not be formally incorporated into any domestic legal system. States may decide in an international agreement to create a tribunal that will formally be part of a domestic court system, meaning that the tribunal will derive the authority to exercise its judicial function from domestic law. Despite being created on an international law basis with the involvement of multiple States, such a tribunal will be  domestic. The Extraordinary African Chambers in the Senegalese Courts is an example of a domestic court created by an international agreement between Senegal and the African Union (Agreement, Article 1(1)). The Statute of the Extraordinary African Chambers, while being an annex to an international agreement, stipulated that the Extraordinary African Chambers were to be embedded “within the [Senegalese] courts” (Statute, Article 2) which draw their judicial powers from the Senegalese law. Similarly, the Kosovo Specialist Chambers, whose creation was agreed on in an international agreement, is also a domestic court formally part of the Kosovar legal system, deriving its judicial powers from a municipal law adopted by Kosovo’s legislature (Law on SC and PO, Articles 2(1) and 3). 

As another example, the Extraordinary Chambers in the Courts of Cambodia (ECCC) are, as the name indicates, domestic courts of Cambodia. That the U.N. was closely involved in the creation of the ECCC does change this fact. The U.N. Secretary General, at the request of the United Nations General Assembly, negotiated a draft Agreement between the U.N. and Cambodia concerning the prosecution under Cambodian law of crimes committed by the Khmer Rouge. The General Assembly approved, in a resolution, the agreement whose purpose was to regulate the cooperation between the U.N. and Cambodia in prosecuting relevant crimes (Article 1). But the Extraordinary Chambers were created based on the Cambodian Law on the Establishment of the Extraordinary Chambers implementing the Agreement (Article 2 (2)) and “within the existing court structure of Cambodia” (Agreement, preamble, para 4; Law, Article 2). The ECCC is therefore formally part of the court system of Cambodia and exercises judicial powers on the basis of Cambodian domestic law. 

An international tribunal is therefore a tribunal that is (1) created with the involvement of two or more States based on an international legal instrument, and (2) not formally incorporated into a domestic legal system. That the jurisdiction of such a tribunal may cover crimes under domestic law (SCSL Statute, Articles 1 and 5), that such a tribunal is empowered to apply domestic law (STL Statute, Article 2), and that its composition includes domestic judges of the State concerned (STL Statute, Article 8) does not make the tribunal any less international. 

Conversely, an ad hoc tribunal incorporated into the domestic court system and deriving from the domestic law its power to exercise judicial function will remain domestic even if injected with numerous international elements. The Kosovo Specialist Chambers is a domestic court even though located outside Kosovo, empowered to apply international law, and composed of only international judges (Law on SC and PO, Article 3(6) and (7), Articles 12, 26). Similarly, the presence of international judges and other personnel in the structure of the ECCC (Agreement, Articles 3, 5, 6; Law, Articles 9, 16, 23), involvement of the U.N. in its creation, or its funding from “voluntary contributions from the international community” does not make the ECCC an international tribunal. 

That said, ad hoc criminal tribunals that combine domestic and international features are often called “hybrid” or “internationalized” tribunals. That denomination does not, however, change their formal legal nature which, as explained below, depending on the constituent instrument and the legal basis for the exercise of their judicial powers, remains either domestic or international (for an in-depth discussion, see Roger O’Keefe, International Criminal Law, Chapter 3).

In the case of Ukraine, an ad hoc tribunal created based on a bilateral treaty between Ukraine and the CoE, or a multilateral treaty between Ukraine and individual CoE member States will be international, provided the tribunal is not formally incorporated into the domestic court system of Ukraine or any other State. That this tribunal may be empowered to apply the domestic law of Ukraine, cooperate with Ukraine’s prosecuting authorities, or include Ukrainian judges will not change its formal international legal character. Conversely, if the agreement provides that the tribunal is anchored in Ukraine’s or in any other State’s court system, it will be domestic even if it is empowered to apply international law, located outside Ukraine or that other State, and includes foreign judges. 

A ‘Truly International’ Tribunal

Views differ as to whether the international character of a tribunal is sufficient to overcome personal immunities of acting political leaders of the State, namely head of State, prime minister, and the minister of foreign affairs. 

One view is that, absent the waiver of the immunities by the State concerned or a U.N. Chapter VII decision of the Security Council, the international nature of a tribunal alone does not suffice (e.g., Advisory Committee on Public International Law, pp. 13-14). A different view, now reflected in the findings (Jordan Referral Appeals Judgment, paras 113-115) and recent practice (Putin Arrest Warrant) of the ICC, is that the personal immunities of a sitting head of State do not serve as a bar to the jurisdiction of an international criminal court. Between these two positions, the ICC practice better reflects the current state of international law on personal immunities.  

“International” in this context means, however, something more than a tribunal established with the involvement of multiple States and independent of any country’s  domestic legal system. According to the ICC, an international court is a tribunal that acts “on behalf of the international community as a whole” (Jordan Referral, para 115). The ICC considered itself, a court created by a multilateral treaty that came into force once ratified by 60 States, such an international tribunal. So too are tribunals established by a resolution of the Security Council under Chapter VII of the U.N. Charter (e.g., ICTY, ICTR, STL) or tribunals based on an agreement between the relevant State and the U.N. following a decision of the Security Council (e.g., SCSL). According to the SCSL, when deciding to establish a court in exercise of its function to maintain and restore international peace and security under the Chapter VII of the U.N. Charter, the Security Council acts on behalf of all 193 U.N. member States (Decision on immunity, para 38). The agreement between the U.N. and Sierra Leone to establish an ad hoc criminal tribunal following a decision by the Security Council is therefore an expression of the will of the international community, which makes the SCSL a “truly international” court (ibid, para 38).  

One reason that the personal immunities of a head of State do not bar prosecution by an international criminal court is, the ICC explained, that international courts do not act on behalf of a particular State or States (Jordan Referral, para 115). In contrast to a domestic court, an international criminal court is not an expression of the exercise of the sovereign power of the State. Consequently, the principle of sovereign equality of States which underpins the international law rules on immunities, does not apply to international criminal courts (ibid, para 115). 

“A truly international court” acting on behalf of the “international community as a whole” remains a vague notion. The notion of a tribunal not acting on behalf of a particular State or States, while also imprecise, is easier to grasp. In addition, some indicators can also be inferred from the abovementioned views and practice of the ICC and the SCSL: An international tribunal acts in the name of the international community and not on behalf of a particular State or States if it is created by a multilateral agreement between at least 60 States (the number of ratifications required for the entry into force of the Rome Statute of the ICC according to its Article 126(1)) or with the involvement of the Security Council acting in exercise of its function to maintain and restore international peace and security (ICTY, ICTR, SCSL, STL). It has also been suggested that a tribunal that receives endorsement from the General Assembly can also be “truly international” (e.g. Alexandre Skander Galand).

The options involving the Security Council and General Assembly aside, an international tribunal created based on a multilateral treaty open to any State and counting at least 60 States can arguably be considered as sufficiently, or “truly,” international. After all, that number was sufficient for the ICC to be established as a court acting on behalf of the international community (e.g., analysis by Astrid Reisinger Coracini and Jennifer Trahan). A tribunal based on a treaty concluded by roughly one third of U.N. member States (60 out of 193) can hardly be said to be acting on behalf of a particular State or States. In addition, similar to the ICC Statute, a treaty establishing a sufficiently international criminal court must be open to any State from any region to join either during the negotiations stage or afterwards. In summary, the ICC example suggests that for a tribunal to be considered “truly international”, the agreement establishing the tribunal must have at least 60 States parties and must be open to any State to join. 

A multilateral treaty between Ukraine and the other CoE member States can have a maximum 46 State parties. An agreement between Ukraine and the CoE as such can arguably represent the will of all 46 member States provided the support for the special tribunal by all the member States is made clear in the process of the agreement negotiations and conclusion. In both proposals, however, the agreement must necessarily be made open to States from outside Europe in order to reach 60 ratifications. Opening of the CoE treaties to non-member States is a usual practice: 153 out of 223 existing CoE treaties are open to non-member States and more than 100 non-member States have observer status in or are parties to the so called “enlarged agreements” (CoE outreach beyond membership). The CoE indeed considers the option of an agreement open to non-member States in case of the special tribunal. More specifically, the CoE Committee of Ministers authorized the Secretary General to examine the possible options for an enlarged agreement on support, financing, and administration of the special tribunal (Decisions, para 5).  


Since the start of Russia’s full-scale invasion, Ukraine has advocated for the creation of an international tribunal for the crime of aggression committed on its territory. A special tribunal based on a treaty between Ukraine and the CoE, or the CoE member States, is a promising prospect. A tribunal created by such a treaty, even if empowered to apply domestic law, will be international if it is not formally incorporated into the domestic court system of Ukraine or another State. Conversely, if a treaty provides that the special tribunal is part of a domestic legal system, none of the international elements injected into the tribunal will turn it into an international criminal court. 

What is more, an international tribunal based on a treaty with the CoE or its member States can arguably be considered sufficiently international to overcome the personal immunities of the acting State leaders if its founding treaty, similarly to the Rome Statute of the ICC, is open for any state in the world to participate in the negotiations or join afterwards, and is conditioned to come into force upon its ratification by at least 60 States. Finally, the involvement of the CoE – an intergovernmental international organization – in the creation of the special tribunal, together with potential accession of non-member States from outside Europe to the treaty establishing the special tribunal, will contribute to greater legitimacy of the effort to prosecute the crime of aggression committed in Ukraine. 

IMAGE: On Feb. 23, 2024, The Berlaymont, headquarters of the European Commission, in Brussels, Belgium, is lit in blue and Yellow, the colors of the Ukrainian flag, to mark the two year anniversary of Russia’s large-scale invasion of Ukraine. (Photo by Thierry Monasse via Getty Images)