Calling for the safe return of the children to Ukraine, the parliament said "the documented evidence of this practice matches with the international definition of genocide".

Ukrainian President Volodymyr Zelensky hailed the resolution as an "important" decision that will help "hold Russia and its leaders to account".

The deportation of Ukrainian children is one element of "Russia's attempt to erase the identity of our people, to destroy the very essence of the Ukrainian people", he said in his evening address.

On March 17, the International Criminal Court (ICC) issued an arrest warrant for Russian President Vladimir Putin, citing the "unlawful deportation" of children.

The Hague-based court also issued a warrant for Maria Lvova-Belova, Russia's presidential commissioner for children's rights.

Kyiv said in mid-April that more than 16,000 Ukrainian children had been "abducted" and taken to Russia since the start of the invasion on February 24 last year. It said many of them had been placed in care homes.

Thursday's resolution at the Council of Europe's parliament said there was "evidence that deported children had faced a process of 'russification' through re-education in Russian language, culture and history".

"These transfers of Ukrainian children were 'clearly being planned and organised in a systematic way' as state policy," said the resolution, with the aim of "annihilating every link to and feature of their Ukrainian identity".

The Parliamentary Assembly of the Council of Europe (PACE) called on the United Nations and the Red Cross to be granted access so they could gather information on the children concerned.

The 1948 convention on genocide refers to the forcible transfer of children among its defining criteria.

Following its invasion of Ukraine, Russia was expelled from the Council of Europe.

The organisation, which comprises 46 member states, was set up to monitor and uphold human rights in Europe.