Ukraine and pro-Russian separatist rebels have begun swapping prisoners under the terms of a preliminary peace deal signed in Minsk on December 24.
Russian news agencies reported that the exchange was taking place in a neutral location some 30 kilometers north of the rebel-held city of Donetsk on December 26.
The prisoner exchange was expected to involve more than 220 separatist gunmen and some 150 Ukrainian soldiers.
State security sources in Kyiv said the separatists would still be holding about 500 government soldiers after the exchange.
Earlier, officials in Belarus said a key round of peace talks between Ukraine and pro-Russian rebels -- tentatively scheduled for December 26 -- had been canceled.
Kyiv had hoped the meeting would lead to the signing of a final peace deal on ending fighting in eastern Ukraine.