Former war crimes prosecutor Carla Del Ponte has called for the International Criminal Court to quickly issue an arrest warrant for Russian President Vladimir Putin over actions in Ukraine.

“Putin is a war criminal,” Del Ponte, who came to prominence investigating war crimes in Rwanda and the former Yugoslavia, said in an interview with the Le Temps daily, published Saturday.

The 75-year-old Swiss national said that international arrest warrants for Putin and other high-level Russian officials were needed to hold them responsible for the war crimes committed since Moscow launched its full-scale invasion of Ukraine on February 24.

Just over five weeks into the invasion, thousands have been killed and millions displaced as parts of Ukraine have been reduced to rubble.

Del Ponte, who also served for years on the UN commission probing rights abuses in Syria’s war, stressed that issuing an arrest warrant was an important signal “that investigative work has been done.”

“It is the only instrument that exists that makes it possible to arrest the perpetrator of a war crime and bring them before the ICC,” she told Le Temps.

Del Pont acknowledged that an arrest warrant did not necessarily mean Putin would be taken into custody.

“If he remains in Russia, that would never be the case. But it would be impossible for him to leave his country, and it would be a strong signal that he has many states against him.”

The Hague-based ICC’s chief prosecutor opened an active probe into possible war crimes in Ukraine on March 3, after obtaining the backing of more than 40 states that are party to the court.

Del Ponte said her experience as chief prosecutor for the International Criminal Tribunal for the former Yugoslavia brought her hope that Putin, like former Yugoslav president Slobodan Milosevic, could one day be arrested and charged with war crimes.

And “incriminating evidence must also be found against high-level political and military officials,” she said.

“The difficulty is precisely reaching the top of the command chain to identify who planned, ordered and executed the war crimes.”

Ukraine is not a signatory to the Rome Statute treaty which established the ICC but it did in 2014 officially recognise the court’s jurisdiction for crimes committed on its soil.

Russia withdrew its signature from the Rome Statute in 2016.