More than 2,400 children from Ukraine aged between six and 17 years old have been taken to 13 facilities across Belarus since Russia's invasion of Ukraine, research published by Yale University said on Thursday.

Ukraine's prosecutor general said in May that he was investigating the alleged role of Belarus in the forced transfer of more than 19,000 identified children from Russian-occupied territories since the conflict broke out, including to Russia.

The total number is estimated by some experts and organisations to be far higher.

The findings by the Humanitarian Research Lab at Yale School of Public Health, which receives US State Department funding, shared with Reuters are the most extensive to date about the alleged role of Belarus in the Russian relocation program for Ukrainian children.

Russia has said previously that it is offering humanitarian aid to those wishing to flee Ukraine voluntarily and rejects accusations of war crimes.

The press service of Russia's Children's Rights Commissioner, who oversees the relocation of children from occupied Ukraine, and Belarus' foreign ministry did not immediately respond to requests for comment on the research.

"These revelations of Belarusian involvement are part of a broader campaign directed by Russia," the US State Department said in a statement.

"The United States will continue to pursue accountability for actors involved in abuses connected with Russia's war against Ukraine."

Among the key findings detailed in the 39-page report were that children had been transported from at least 17 cities in Ukraine's Donetsk, Luhansk, Kherson, and Zaporizhzhia regions in what Yale researchers described as an ongoing practice.

More than 2,000 children Yale identified were transported to the Dubrava children's centre in Belarus' Minsk region between September 2022 and May 2023, it said, while 392 children were taken to 12 other facilities.

"Russia's systematic effort to identify, collect, transport, and re-educate Ukraine's children has been facilitated by Belarus," the report said.

"Russia's federal government and Belarus' regime have been working together to coordinate and fund the movement of children from Russia-occupied Ukraine through Russia to Belarus."

Transports to Belarus through Russia were "ultimately coordinated" between Russian President Vladimir Putin and Belarus leader Alexander Lukashenko, it added.

The International Criminal Court in The Hague issued an arrest warrant for Russia's Putin in March. It accused him and Children's Rights Commissioner Maria Lvova-Belova of the war crime of illegally deporting hundreds of children from Ukraine.

Taking children under the age of 18 across a border without the consent of a parent or guardian is prohibited under international humanitarian law.

Ukraine's war crimes prosecutors have said they are investigating the deportations as potential genocide.

The Genocide Convention specifies five acts that could each constitute the crime, if committed with genocidal intent, including forcibly transferring children out of their group.

Ukraine's foreign ministry and the office of the prosecutor general, which oversees war crimes investigations, did not immediately respond to requests for comment.

Lukashenko approved the use of state organizations to transport children from Ukraine to Belarus and finance their transportation, the Yale report said. Once in Belarus, children have been subjected to military training and re-education, it said.

It is unclear how many of the children identified by Yale's research remain in Belarus.