The United States on Tuesday threw support behind a special international tribunal to try Russia for "aggression" against Ukraine, building momentum to prosecute the crime for the first time since the aftermath of World War II.
The European Union has backed a special tribunal, which could bring fresh charges against President Vladimir Putin and would be the latest legal salvo after the International Criminal Court issued an arrest warrant for him over alleged war crimes.
The State Department said that the United States would work with allies to set up a "special tribunal on the crime of aggression" over Russia's February 2022 invasion of its neighbor.
"We envision such a court having significant international support -- particularly from our partners in Europe -- and ideally located in another country in Europe," State Department spokesman Vedant Patel told reporters.
Beth Van Schaack, the US ambassador-at-large for global criminal justice, said the United States wanted the court to have international personnel and resources.
That "will provide the clearest path to establishing a new tribunal and maximizing our chances of achieving meaningful accountability," she said in a speech Monday at the Catholic University of America.
She said the United States was "committed" working with other countries to provide resources for such a tribunal "in a way that will achieve comprehensive accountability for the international crimes being committed in Ukraine."
It was the first time that the United States -- which has fraught relations with the International Criminal Court -- has explicitly supported a special tribunal on Ukraine.
The European Union in November floated the idea of a tribunal, which was backed formally in January by a vote of the European Parliament.
- World War II legacy -
Czech Foreign Minister Jan Lipavsky, speaking virtually Tuesday to a US-led democracy summit, said his country "strongly advocates" the special tribunal, saying that Putin's invasion brought memories of Czechoslovakia's forced land concessions to Germany in 1938.
The crime of aggression, then known as a crime against peace, was last prosecuted in the aftermath of World War II and formed a basis of the Nuremburg and Tokyo trials of officials from Nazi Germany and imperial Japan.
The International Criminal Court since 2018 has had jurisdiction over the crime of aggression, but legal experts say it cannot prosecute Russia as the country, like the United States, has not joined the Rome statute that set up the tribunal in The Hague.
Nations not part of the court can still be referred by a vote of the UN Security Council -- where Russia would be certain to exercise its veto power.
The idea of a special tribunal was first promoted shortly after the Ukraine invasion by Britain's former prime minister Gordon Brown, alongside legal scholars.
Brown, in a March 2022 petition, said it may be "easier to establish responsibility" for the crime of aggression than for individual war crimes as there was "so clearly a gross violation of the United Nations Charter."
The International Criminal Court's arrest warrant stems from accusations that Russia unlawfully deported Ukrainian children.
US Secretary of State Antony Blinken has balked on whether the United States in theory would arrest Putin. Under a law of Congress, the United States is restricted from cooperating closely with the court, seeking to avoid a precedent for prosecuting Americans.