Dozens of prisoners are exchanged between Ukrainian forces and pro-Russian separatists in the the eastern city of Donetsk.
The exchange is part of a ceasefire deal that has largely held in recent days.
International observers from the OSCE monitored the swap.
Dimitry Nikonov says he was taken prisoner for declaring he was mayor of Nikolaev and calling for the separation of the city.
(SOUNDBITE) (Russian) SELF-PROCLAIMED NIKOLAEV 'PEOPLE'S MAYOR', DMITRY NIKONOV, SAYING:
"At one of the rallies, I was chosen for the position of the people's mayor of Nikolaev, and because of this they accused me of a criminal deed."
There is no exact figure of the number of prisoners held by both sides in the months-long conflict that has claimed more than 3,000 lives.
