A new European Union proposal for an international tribunal to try Russian aggression in Ukraine has received mixed reviews — prompting a thumbs up from Kyiv and rights advocates but doubts from experts about its feasibility and whether it will receive broad-based acceptance.

“Russia must pay for its horrific crimes, including for its crime of aggression against a sovereign state,” said European Commission President Ursula von der Leyen Wednesday, laying out arguments for establishing a new, United Nations-backed court. “We are ready to start working with the international community to get the broadest international support possible for this specialized court.”

The United Nations-backed International Criminal Court — also known as the ICC — in the Netherlands is already looking into alleged Russian war crimes and crimes against humanity in Ukraine, as well as possible Ukrainian atrocities. Russia has denied committing war crimes and accused the international community of ignoring abuses by Ukrainian forces.

Special U.N.-backed tribunals aren’t new. The body proposed by von der Leyen, if ever realized, would focus on Russian aggression in Ukraine.

First lady points to thousands of crimes

The Ukrainian government has been quick to support the idea. Visiting a London exhibition this week on alleged Russian war crimes, Ukraine’s first lady Olena Zelenska called for justice.

She said more than 40,000 Russian crimes had been registered in Ukraine. Look at the photos at the exhibition, she told her audience, and abstract ideas of war in Ukraine will become real.

Moscow has dismissed the idea of a new war crimes tribunal as having no legitimacy. Experts suggest it would be challenging to establish one.

“My reading of what Ursula von der Leyen said is that the EU doesn’t take for granted that there would be overwhelming international support — and that it recognizes there has to be a sort of campaign to win support for the idea,” said Anthony Dworkin, a policy fellow specializing in human rights and justice at the European Council on Foreign Relations, a think tank.

Proposal needs support from developing nations

Brussels will especially need backing from developing countries in Africa and elsewhere, said Dworkin.

“I think it’s very important that that should be done, rather than European countries kind of short-circuiting the attempt to win international legitimacy for the idea by just setting it up themselves,” he said.

Even if it’s up and running, such a tribunal could face obstacles if, for example, Russian President Vladimir Putin or other Russian officials face war crimes charges yet are still welcome to visit some nations. That was the case with Sudan’s former leader, Omar al-Bashir, who traveled to multiple countries despite ICC arrest warrants.

Charges against high-level Russian officials may also complicate any future Western efforts to end the war in Ukraine.

“A court is supposed to be politically independent,” said Dworkin. “And therefore, you wouldn’t for instance expect — if there is a kind of negotiation at the end of the conflict — that the charges would be somehow dropped as part of the negotiation. The charges will persist.”