The Ukrainian government and pro-Russian rebels in the country's east appeared ready on Friday to exchange prisoners.
President Petro Poroshenko said in a speech that there was great hope that a severely wounded prisoner, Volodymyr Zhemchugov, would be returned to the Ukrainian side as soon as Saturday.
Meanwhile, the Russia-based Interfax news agency reported that there was a high possibility that Zhemchugov and a member of the Ukrainian Security Service, Yury Suprun, would be exchanged for members of the two major rebel groups.
The news agency cited an undisclosed source as saying that the exchange would happen on Saturday.
Earlier this week the Ukrainian government agreed to a new, rebel-proposed ceasefire following an abrupt escalation of tensions between Russia and Ukraine in recent weeks.
More than 9,600 people have been killed in the conflict in Ukraine's two easternmost regions, Donetsk and Luhansk, according to estimates released this week by the United Nations.
The conflict began two years ago when Ukraine ousted its pro-Russian president amid mass protests calling for closer ties with the West.