The move was part of an agreement brokered earlier this month at a summit of the leaders of Ukraine, Russia, Germany and France.

Iran and the U.S. conducted a prisoner exchange Saturday that saw a detained Princeton graduate student released for an Iranian scientist held by America, marking a potential breakthrough between Tehran and Washington after months of tensions.

Russia and Ukraine on Saturday exchanged 35 prisoners each to the other country, a move that could be a significant step toward easing Russia-Ukraine relations and raise chances for resolving the conflict in Ukraine's east.