As part of the swap, Kiev was expected to hand over to separatists several riot policemen suspected of killing protesters during a pro-Western uprising in 2014, in a move that sparked public anger.

"At the Mayorske checkpoint the process of releasing detained persons has begun," the official Twitter account of the Ukrainian president said.

It was still unclear how many people were involved in the exchange.

A representative of the separatist stronghold of Donetsk, Daria Morozova, said earlier that separatists would get 87 prisoners, while 55 people would be handed over to Kiev.

The two sides were seen preparing the exchange prisoners early Sunday, with vehicles arriving near the village of Odradivka, some 10 kilometres (6 miles) from the self-proclaimed Donetsk People's Republic, an AFP correspondent reported from the scene.

The location was guarded by uniformed men with machine guns.

Russian President Vladimir Putin and Ukrainian leader Volodymyr Zelensky held their first face-to-face talks in Paris on December 9 and agreed some measures to de-escalate Europe's only active war.

Ties between Ukraine and Russia were shredded after the bloody 2014 uprising ousted a Kremlin-backed regime.

Moscow went on to annex Crimea and support insurgents in eastern Ukraine, who launched a bid for independence in 2014. Since then more than 13,000 people have been killed in the conflict.