(AFP) - The International Criminal Court on Friday announced an arrest warrant for Russian President Vladimir Putin on the war crime accusation of unlawfully deporting Ukrainian children.

The Hague-based ICC said it had also issued a warrant against Maria Lvova-Belova, Russia's presidential commissioner for children's rights, on similar charges.

Moscow dismissed the orders as "void." Russia is not a party to the ICC so it was unclear if or how Putin could ever end up in the dock.

War-battered Ukraine welcomed the ICC announcement, with President Volodymyr Zelensky hailing the "historic decision."

The court's shock notice came hours after other news with the potential to significantly impact Russia's war on Ukraine, including a Moscow visit from Chinese leader Xi Jinping and more fighter jets for Kyiv's forces.

More than 16,000 Ukrainian children have been deported to Russia since the February 24, 2022 invasion, according to Kyiv, with many allegedly placed in institutions and foster homes.

ICC prosecutor Karim Khan told AFP that Putin was now liable for arrest if he set foot in any of the court's more than 120 member states.

He said the arrest warrants were "based upon forensic evidence, scrutiny and what's been said by those two individuals".

"The evidence we presented focused on crimes against children. Children are the most vulnerable part of our society," said Khan.

The ICC said judges found there were "reasonable grounds" to suspect Putin's criminal responsibility and grant Khan's application for the warrants, which were made back on February 22.

ICC President Piotr Hofmanski said the execution of the warrants "depends on international cooperation".

- 'Historic decision' -

During a meeting with Putin in mid-February, Lvova-Belova said she adopted a 15-year-old child from the devastated Ukrainian port city of Mariupol.

"Now I know what it means to be a mother of a child from Donbas -- it is a difficult job but we love each other, that is for sure," she told Putin.

She added that "we evacuated children's homes into safe areas, arranged rehabilitation and prosthetics for them and provided them with targeted humanitarian assistance."

The arrest warrant for Putin, a sitting head of state of a UN Security Council member, is an unprecedented step for the ICC.

Set up in 2002, the ICC is a court of last resort for the world's worst crimes, when countries cannot or will not prosecute suspects.

Prosecutor Khan launched an investigation into alleged war crimes and crimes against humanity in Ukraine just days after Russia's invasion.

Khan recently posted pictures from a visit to Ukraine alongside empty cots in an empty children's care home, and said that investigating alleged child abduction was a "priority".

"It's poignant," he said. "One sees empty cribs and empty beds juxtaposed with paintings by those children on the walls."

Zelensky, who met Khan on his visit, welcomed the arrest warrants for his nemesis in Moscow.

"A historic decision from which historic responsibility will begin," Zelensky said.

Ukraine's Western allies also hailed the move.

US President Joe Biden said the warrant was "justified," and "makes a very strong point," while noting that the United States is not a member of the ICC.

"There is no doubt that Russia is committing war crimes and atrocities in Ukraine, and we have been clear that those responsible must be held accountable," a State Department spokesperson said. "The ICC Prosecutor is an independent actor."

Britain called the decision "welcome" and the European Union said it was "just the start." Human Rights Watch said it was a "big day for the many victims" of Russian forces.

- 'Void' -

The Kremlin dismissed the warrants.

"Russia, just like a number of different countries, does not recognise the jurisdiction of this court and so from a legal point of view, the decisions of this court are void," Kremlin spokesman Dmitry Peskov told reporters.

Former Russian president Dmitry Medvedev compared the warrants to toilet paper, while foreign ministry spokeswoman Maria Zakharova said they "have no meaning" for Russia.

The ICC's Khan however said there were "so many examples of people that thought they were beyond the reach of the law".

"Look at (Slobodan) Milosevic or Charles Taylor or (Radovan) Karadzic or (Ratko) Mladic," he said, referring to a series of war criminals from the former Yugoslavia, and former Liberian president Taylor, who have faced justice.

Earlier in the day, Beijing and Moscow announced that Chinese leader and strategic ally Xi would be in Russia next week to sign accords ushering in a new era of ties.

The United States has accused China of mulling arms shipments to support Russia's campaign -- claims Beijing has strongly denied.

The arrest warrants come a day after UN investigators said Russia's forced transfer and deportation of Ukrainian children to areas under its control amounts to a war crime.

The investigators said parents and children had spoken of youngsters being informed by Russian social services that they would be placed in foster families or adopted.

Neither Russia nor Ukraine are members of the ICC, but Kyiv has accepted the court's jurisdiction and is working with Khan's office.

Russia denies allegations of war crimes by its troops. Experts have said it is unlikely it would ever hand over any suspects.

With fighting still raging in Ukraine, Kyiv welcomed the news Friday that Slovakia will donate 13 MiG-29 warplanes.

Ukraine has long requested fighter jets from Western allies, although it is seeking primarily modern US-made F-16s.

© Agence France-Presse