Ukraine’s Human Rights Commissioner Dmytro Lubinets said this at a briefing, Ukrinform reports.
"We have evidence that both the forced transfer of Ukrainian children, civilian hostages and prisoners of war took place through the territory of Belarus with the direct participation of the Belarusian authorities," he said.
According to the ombudsman, Russia is currently holding more than 27,000 civilians hostage.
On 24 May, the Office of the Prosecutor General reported that Ukraine was investigating the possible role of Belarus in the forced deportation of children from the temporarily occupied territories.
On 17 March, the International Criminal Court in The Hague issued an arrest warrant for Russian President Vladimir Putin. He is accused of the 'war crime of unlawful deportation of children’.