war exchange in Donetsk region, Ukraine
Men get off buses before reuniting with servicemen and officials of the self-proclaimed republics during the exchange of prisoners of war between Ukraine and the separatist republics near the Mayorsk crossing point in Donetsk region, Dec. 29, 2019.

Ukrainian authorities and Russia-backed separatists in eastern Ukraine have completed a prisoner swap, the office of Ukraine's president said on Sunday.

"Mutual release of detained persons has ended," the presidential office said in a tweet, adding that 76 people had been released and transferred to the government.

It wasn't clear how many prisoners had been returned to the separatists.

Earlier, the UNIAN news agency quoted had quoted a representative of Donetsk separatists as saying that Ukrainian side was expected to hand over 87 people, while the separatists were set to swap 55.

It marks the second major prisoner exchange involving Ukrainians caught up in the conflict in four months.

A Ukrainian citizen is welcomed upon his arrival following the exchange of prisoners of war (POWs) between Ukraine and the separatist republics near the Mayorsk crossing point in Donetsk region, Dec. 29, 2019.

The exchange took place near the village of Horlivka near Mayorske, some 35 kilometers north of Donetsk.

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.

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.

The move is not without controversy in Kyiv.

According to AFP, the government is expected to hand over to the separatists several riot police officers suspected of killing protesters during a pro-Western uprising in 2014.

Families of the victims of the riot police wrote on Facebook in an open letter to Zelenskiy, warning that the release of the men could lead to a "wave of protests."

"We would like to inform you that these people are neither participants nor victims of the conflict in eastern Ukraine," they wrote.

The conflict in the region known as the Donbas is one of the biggest challenges facing Zelenskiy, who campaigned on a vow to end the conflict. He was inaugurated on May 20.

The United States and European Union have imposed sanctions on Russia for its support of the separatists in eastern Ukraine and for the seizure and annexation of Ukraine’s Crimea region.