European military observers held captive in Slaviansk in eastern Ukraine were released on Saturday, the town's pro-Russian separatist leader said, characterising the move as voluntary and made to coincide with his birthday.
"As I promised them, we celebrated my birthday yesterday and they left. As I said, they were my guests," Vyacheslav Ponomaryov said, adding that 12 people had been freed, including Europeans and Ukrainians.
Eight observers who were in Ukraine under the auspices of security watchdog the Organization for Security and Cooperation in Europe (OSCE) were seized last week by separatists who said they had found a spy with them. They later released one on medical grounds.
Read MoreThe faces of the Ukrainian conflict
It was not clear who else was among those released, but the group had been accompanied by at least one translator.
Ponomaryov said Russian envoy Vladimir Lukin, who arrived in eastern Ukraine on Friday, had helped negotiate their release.
"His visit was one of the important factors," he said.
Kiev and the West had criticized Moscow for failing to help with the captives' release, saying Russian officials had not even condemned the detentions.
Follow us on Twitter: @CNBCWorld