Ukrainian Prosecutor-General Iryna Venediktova, who is overseeing multiple war crimes inquiries in her country, says an investigation is ongoing in the forcible deportation of children to Russia as she looks to build a genocide indictment against Moscow.

Venediktova told Reuters in an interview published on June 3 that Ukraine already has “more than 20 cases about the forcible transfer of people” to Russia since the invasion began on February 24.

She added that focusing on the removal of children offered the best way to secure the evidence needed to meet the rigorous legal definition of genocide.

“From the first days of the war, we started this case about genocide,” she said.

“That’s why this forcible transfer of children is very important for us,” she added.

Under the 1948 Genocide Convention, the forced mass deportation of people — and in particular the forcible transfer of children — during a conflict is designated as a war crime.

Venediktova did not say how many children she suspects had been forcibly transferred from Ukraine to Russia, but Ukraine’s ombudswoman, Lyudmyla Denisova, said in May that Russia had relocated more than 210,000 children during the conflict.