Ukraine's human rights ombudsman Dmytro Lubinets said Thursday Moscow had stopped swapping prisoners of war with Kyiv.
The two warring sides have carried out many rounds of prisoner exchanges during Moscow's 21-month long invasion, but in the latter half of this year the process stalled.
"Exchanges are not taking place because Russia does not want them to," Lubinets said on Telegram.
"All initiatives, wishes and actions of Ukraine to return its defenders from captivity are met with Russian reluctance to return even its own citizens," he said.
Thousands of prisoners of war are believed to be held by both sides.
Lubinets alleged Russia wanted its people to believe Ukraine was "not doing anything to return soldiers."
Ukraine said in August that it had brought back some 2,600 of its captive soldiers in around 50 exchanges with Russia since the start of the invasion in February last year.
Earlier this month, Lubinets announced it had opened a new camp for Russian prisoners of war and plans for building another one, with the number of Russian captives increasing as the war drags on.
Moscow has in recent weeks handed out heavy sentences to Ukrainian prisoners of war it holds captive.