Ukraine and pro-Russian separatists agreed on a prisoner exchange Friday but could not come to a deal to restart peace negotiations in Belarus. Kiev will give the rebels 225 of their fighters, while the rebels will hand over 125 Ukrainian soldiers, according to Reuters.

"We've prepared 225 people, which we will hand over. The main thing is for this not to fall through now," Markiyan Lubkyvsky, the head of Ukraine’s SBU state security service, told Reuters. The rebels are believed to be holding about 600 prisoners.

Peace talks were last held on Wednesday, according to Agence France-Presse. A Belarussian official told AFP that the two sides couldn’t agree to meet Friday in Minsk. The Wednesday meeting among Ukraine, Russia, the separatists, and the Organization for Security and Cooperation in Europe ended after five hours.

“There will be no contact group meeting today,” Dmitry Mironchik of the Belarussian Foreign Ministry told AFP.

Tensions between Ukraine and Russia flared after Moscow annexed the Ukrainian territory of Crimea in March. Pro-Russian separatists in eastern Ukraine then started battling the Ukrainian army in a conflict that has so far led to more than 4,700 deaths, according to Reuters. A cease-fire agreement was struck in September, but has been repeatedly broken. About 1,700 people have been killed since the ceasefire. One of the goals of the peace talks is to reinforce the ceasefire, according to AFP.

The annexation of Crimea was preceded by protests in Ukraine that led to the ouster of pro-Russian President Viktor Yanukovych in February. Petro Poroshenko, who is closely aligned with the West, is the current Ukrainian leader.

Russia has been accused by Ukraine and the West of instigating tensions in eastern Ukraine, but Moscow denied involvement in the conflict.