Ukrainian authorities and pro-Russian separatists in the war-torn east of the country are expected to swap dozens of prisoners in a front-line operation on Sunday.
Both sides had said earlier this month they would carry out a prisoner exchange by the end of the year, following high-profile peace talks in Paris aimed at de-escalating Europe's only active war.
"The exchange should be tomorrow. We're all waiting for it," Ukrainian President Volodymyr Zelenskyy said on Saturday, calling it "the most difficult task this year".
Earlier, a spokeswoman for the self-declared rebel republic of Donetsk, Daria Morozova, announced that there was an agreement for the swap.
She said two separatist territories Donetsk and Lugansk will get 87 prisoners, while 55 others will be handed over to Kyiv, without giving details on the identity of those involved.
The prisoner exchange is expected to take place near the town of Gorlivka in the separatist-held Donetsk region in eastern Ukraine's industrial heartland.
Russian media reported that the operation will take place on the front line.
The swap would come three months after Ukraine carried out a long-awaited exchange with Russia of 35 prisoners each.
More than 13,000 people have been killed since pro-Russia fighters in eastern Ukrainelaunched a bid for independence in 2014, sparking the conflict.
Details of Sunday's exchange were scarce, with officials saying that lists of prisoners were still being agreed.
The Organization for Security and Co-operation in Europe (OSCE) Special Representative, Martin Sajdik, confirmed that preparations for the swap were under way.
At the Paris summit this month, the leaders of France, Germany, Russia and Ukraine agreed to implement a full ceasefire and proceed with a new withdrawal of forces from conflict zones by March 2020.
Russian President Vladimir Putin and his Ukrainian counterpart Zelenskyy also held their first face-to-face talks and agreed on measures to de-escalate the conflict.
The December 9 summit was the first of its kind in three years.
Since coming to power in May, comedian-turned-President Zelenskyy, 41, has sought to revive a peace process to end the separatist conflict.
The Kremlin has sent signals that it is ready to work with Zelenskyy, whom Putin has described as "likeable" and "sincere".
Before the summit, Kyiv and separatists completed a partial troop pullback.
French President Emmanuel Macron said at the time of the Paris meeting a new summit would be held in four months to take stock of progress on ending the conflict.
Countries have sought to revive accords signed in Minsk in 2015 that call for the withdrawal of heavy weapons, the restoration of Kyiv's control over its borders, wider autonomy for Donetsk and Lugansk, and the holding of local elections.
However, there was no sign of warmth between the leaders of Ukraine and Russia in Paris and many doubt whether Putin genuinely wants to settle the conflict.
Speaking in Moscow this month, Putin said if Kyiv gets back control of the border in the east, pro-Russian residents of separatist-held territories could be targeted.
Zelenskyy's peace plan has also been strongly criticised by war veterans and nationalists.
Various nationalist organisations even deployed their own troops to the front line in an effort to prevent a troop pullback in line with peace agreements.