Ukrainian President Volodymyr Zelenskiy has said that while a prisoner swap is "supposed to" take place on December 29, the list of individuals to be handed over between central Ukrainian authorities and Russia-backed separatists has not been finalized.

The notion of an "all-for-all" prisoner exchange gained momentum during peace talks in Paris on December 9 among the so-called Normandy Four -- Ukraine, Russia, France, and Germany -- trying to bring an end to the five-year conflict.

"There is supposed to be an exchange [of prisoners] tomorrow," Zelenskiy told journalists during a visit to Ukraine's Ivano-Frankivsk region for a bridge opening on December 28, according to his official website.

"We look forward to this. The verification of all people is not completed yet,” Zelenskiy added.

He went on to call it the year's most difficult task.

The UNIAN news agency quoted a representative of Donetsk separatists as saying that Kyiv was expected to release 87 people and the separatists 55.

But there was no official confirmation of any figures.

There are no definitive, publicly available lists of the prisoners that each side is holding.

This would be the second major prisoner exchange involving Ukrainians caught up in the conflict in four months.

In the last one, Russia and Ukraine traded a total of 70 prisoners in a move that many regarded as progress in efforts to deescalate a war that has killed more than 13,000 people since Moscow forcibly annexed Crimea and Russia-backed gunmen grabbed swaths of eastern Ukraine, including parts of the Donetsk and Luhansk regions, in 2014.

Russia insists it is not a party to the conflict, despite significant evidence that includes communication with separatist leaders, captured Russians, and Russian casualties in the fighting.

A special representative in Ukraine for the Organization for Security and Cooperation in Europe (OSCE) that has monitors in eastern Ukraine and has mediated talks among the parties announced on December 23 that negotiators had "reached an agreement on a mutual release and exchange of conflict-related detainees by the end of the year."

Zelenskiy won the presidency as a political outsider in April pledging to seek an end to the conflict -- which Kyiv and the West blame squarely on Russia -- and clean up rampant corruption for post-Soviet Ukraine's 42 million citizens.

With reporting by AP and UNIAN