The International Criminal Court (ICC) on Monday obtained pledges of financial and technical aid from over 40 countries to investigate crimes in Ukraine, three days after it issued an arrest warrant for Russian President Vladimir Putin.

ICC prosecutor Karim Khan urged countries to find "the stamina to deliver on justice," at the London meeting to discuss boosting support for ICC probes into the war in Ukraine.

The ICC had issued arrest warrants for Putin and his Commissioner for Children's Rights, Maria Lvova-Belova.

They are accused of the war crime of "illegal deportation" of Ukrainian children following Russia's invasion of Ukraine in February 2022.

"Given the indictment of President Putin on Friday, it was very important ... to show our practical support to the ICC," British justice minister Dominic Raab told the gathering.

"We raised over four million pounds and a range of non-financial support and technical support," he added.

Ukrainian President Volodymyr Zelensky added in a video message: "The world must see that no one is above justice."

Moscow responded Monday by announcing it had opened its own criminal inquiry into Khan and several ICC judges, branding the warrants "unlawful".

ICC chief prosecutor Khan told the London conference that the court's investigation into the treatment of Ukrainian children was apolitical, independent and one of "the hallmarks of my office".

"We need to have, collectively, the stamina to deliver on justice," Khan said, calling the conflict in Ukraine a "moment of a reawakening" for the ICC system.

He also decried arguments made that the thousands of Ukrainian children sent to Russia were "humanitarian" evacuations.

The evidence may tell a different story, Khan said, imploring Moscow to "repatriate the children".

"Let them learn their own language in their own schools, instead of being in unfamiliar environments with permanent adoptions by strangers," he added.

- 'Support' -

The meeting hosted by Raab and his Dutch counterpart Dilan Yesilgoz-Zegerius, follows repeated ICC calls for more support for its Ukraine probes.

London has already announced additional funding of nearly £400,000 ($488,000) to help pay for psychological support for witnesses and victims of crimes or to hire additional British experts to reinforce the ICC.

In 2022, co-host the Netherlands dispatched two forensic investigation teams under the banner of the ICC to collect evidence to be used in investigations into crimes committed in Ukraine since the start of Russia's invasion.

Raab, a former lawyer who as a government legal adviser worked on war crimes prosecutions against Serbia's Slobodan Milosevic and Liberia's Charles Taylor, said those at the conference "share the belief that President Putin and the wider (Russian) leadership must be held to account".

"It's absolutely vital that we unite behind the ICC, and that we support the office of the prosecutor with whatever it needs, whether it's resources, whether it's technical expertise, to continue with all of its investigations," he added.

Ukraine's justice minister Denys Maliuska and its prosecutor general, Andriy Kostin, also addressed attendees.

- 'Responsibility' -

The ICC has more than 900 staff with a budget of 169 million euros for 2023, below the court's request of a 175 million euro budget for the year.

Its 123 member states share responsibility for ensuring the court's finances. It also receives voluntary contributions from international organisations, individuals and corporations.