Ukraine has postponed exchanging prisoners and accepting the bodies of killed soldiers for an indefinite period, Kremlin aide Vladimir Medinsky said on Saturday.

"In strict accordance with the Istanbul agreements, on June 6, Russia began a humanitarian operation to hand over to Ukraine more than 6,000 bodies of killed Ukrainian servicemen, as well as to exchange wounded and seriously ill prisoners and prisoners under the age of 25," Medinsky said on Telegram.

He said that 1,212 bodies of killed Ukrainian soldiers were in refrigerated containers at the exchange point. Russia has also handed over to Ukraine the first list of 640 prisoners, categorized as "wounded, seriously ill and young people," in order to begin the exchange, Medinsky added.

There has been no immediate response from Ukraine.