A European military observer detained by pro-Russian activists in the eastern Ukranian city of Slovyansk has been freed.
The officer is one of eight observers to be detained and has apparently been released on medical grounds.
The other seven are still detained.
The self-declared mayor of Slovyansk, Vyacheslav Ponomarev, has said the captured European military observers are hostages "of the situation in Ukraine."
"We perfectly well understand that these gentlemen officers have ended up the victims of a misunderstanding."
Previously Ponomarev accused the group of spying for NATO, saying they could be released in exchange for jailed pro-Russia activists.
The observers are part of a 12-member military verification team deployed by the Vienna-based Organization for Security and Cooperation in Europe.
Russia, an OSCE member, has pledged to take all possible steps to secure the observers' release.
Meanwhile, pro-Russian activists in Slovyansk also captured three Ukrainian security service officers.
Across eastern Ukraine, pro-Russian activists continue to occupy government buildings in a dozen cities.
The U.S. has accused Russia of encouraging destabilizing activities in the region.
The Americans are expected to levy new sanctions against Russia starting from today.
The European Union is also planning more sanctions.
Earlier, Russian President Vladimir Putin said sanctions were hurting the Russian economy, but the damage was not critical.
