The aggression committed by the Russian Federation is more than an attack on Ukraine. It is an attack on the rules-based international order, which is grounded in core provisions of the Charter of the United Nations. Ensuring accountability for the crime of aggression committed against Ukraine would signal that a clearly unlawful and war of occupation/colonisation will have legal consequences - whether in Ukraine or elsewhere. The response of the international community against this bold aggression including through the prosecution of the crime of aggression is therefore of crucial importance for the future of the international legal order.

ICC (The International Criminal Court) can prosecute genocide, war crimes and crimes against humanity committed on the territory of Ukraine because Ukraine submitted to its jurisdiction since 2014. However the ICC’s jurisdiction over the crime of aggression is limited to States that are party to the Rome Statute. Because the Russian Federation is not a party its nationals cannot be held responsible for the crime of aggression before the ICC. While the United Nations Security Council could enable the ICC to exercise jurisdiction over the crime of aggression in the situation in Ukraine by referring it to the Court such a proposal would face the Russian Federation’s veto power and possibly China’s as permanent members of the UN Security Council.

No formal amendment to this effect has been tabled. Moreover, if such an amendment were to be formally submitted, it would take years for it to be adopted and to enter into force. The question of retroactive application would also have to be addressed. Thus, the only way to ensure accountability for the crime of aggression against Ukraine in a reasonable timeframe is an approach outside of the ICC system. Previously, at the Kampala conference discussing the scope of the crime of aggression in the Rome Statute, influential States resisted broader application of the crime of aggression and there is no reason to believe they have changed their position. Nevertheless, support for a special tribunal must be complemented by parallel efforts to amend the ICC’s Rome Statute in order to avoid similar accountability gaps in the future.

The crime of aggression is at the origin of all the other crimes committed in Ukraine. Without the aggression against Ukraine, the other Rome Statute crimes would not have been and continue to be committed. Thus, the crime of aggression is the “supreme international crime” in this situation, and those who are most responsible—the persons in senior political and military leadership positions that decided to commit the aggression—must be held to account.

Various proposals have been made for how to ensure accountability for the crime of aggression against Ukraine. There is one proposal that has the distinct advantage of providing maximum legitimacy and efficiency while avoiding the possible legal pitfalls related to the nature of the crime of aggression as a leadership crime: a special tribunal for the crime of aggression created through an agreement between Ukraine and the United Nations, on the recommendation of the UN General Assembly (UNGA). Alternatives, include an agreement between Ukraine and multi-lateral partners, with possible endorsement from the EU, CoE and/or the UNGA.

Legitimacy: Proceeding through the UN General Assembly allows the international community as a whole to participate in and reaffirm the post-war international legal order. The aggression against Ukraine has been condemned by an overwhelming majority of States in the UN General Assembly in both March and October 2022. A General Assembly resolution recommending the creation of a special tribunal for the crime of aggression would be the logical next step to the General Assembly’s aggression determinations. Efficiency: Negotiations between the United Nations and Ukraine to create a special tribunal for the crime of aggression could proceed immediately after a successful vote on the recommending resolution in the UN General Assembly, and be accomplished expeditiously. And the special tribunal would be a very lean court given its jurisdiction over just one crime – the crime of aggression – and the limited number of persons who could be prosecuted before it, as criminal responsibility for this crime is limited to political or military leaders. Immunities: The definition of the crime of aggression limits criminal responsibility to individuals in leadership positions, defined as persons “in a position effectively to exercise control over or to direct the political or military action of a State.” In order to ensure effective prosecutions, it is therefore essential to overcome personal immunities granted under international law for sitting heads of State, heads of government, and ministers for foreign affairs before foreign domestic criminal courts. This is possible, in particular, due to international law jurisprudence that personal immunities do not represent a bar to the prosecution of senior leaders for international crimes before international criminal courts and tribunals acting on behalf of the international community as a whole, which clearly includes the proposed special tribunal for the crime of aggression on the recommendation of the UN General Assembly.

Such an authorization would fall within the UN General Assembly’s powers as clarified by the International Court of Justice.8 Furthermore, the UN General Assembly has previously authorized the UN Secretary-General to negotiate an agreement with the Government of Cambodia with the view of establishing a criminal tribunal. While the Extraordinary Chambers in the Courts of Cambodia, established as a result, are not the model for the special tribunal for the crime of aggression, the precedent of the General Assembly authorizing negotiations between the United Nations and a UN Member State to establish a court or tribunal is firmly established. The Special Court for Sierra Leone was also created through an agreement between a UN Member State and the United Nations. While in that case, the UN Security Council mandated the UN Secretary-General to act, the Security Council, importantly, in so doing did not act under its Chapter VII authority. These precedents make it clear that an international tribunal for the crime of aggression can be established through an agreement between the United Nations and Ukraine, on the recommendation of the UN General Assembly.