Speaking at a separate news briefing, Russian delegation head Vladimir Medinsky confirmed all sick and heavily wounded prisoners of war, as well as those younger than 25, would be exchanged. No timeframe was given as to when this would happen.

Russia and Ukraine on Monday swapped a first group of captured soldiers -- part of an agreement reached during peace talks that appeared to be in doubt over the weekend.

Russia and Ukraine have agreed to a prisoner exchange and the return of war dead in Istanbul, but peace negotiations have stalled.

Apart from drones, 20 missiles of various types were fired at different parts of Ukraine, according to the air force, which said the barrage targeted mainly central and western areas of Ukraine.