Anti-government protesters on Sunday freed one of the eight international observers that were seized on Friday, as conflicts continued in eastern Ukraine with one television station occupied by protesters.
The released Swedish observer was let go because he had diabetes, said a spokeswoman of the protesters, who added that they had no plan to release the seven others.
The observers, all Europeans, were part of a 12-member military verification team deployed last month by the Vienna-based Organization for Security and Cooperation in Europe (OSCE) in eastern Ukraine to monitor political and security situation in the country following pro-Russia protests in its eastern region.
The protesters claimed to have found a Ukrainian spy travelling with the group, and held the captives in the national security building that has been seized by them in Slaviansk.
Hours before the release, the eight detained observers appeared in front of a press conference while being looked on by their captors.
Col. Axel Schneider from Germany, leader of the observer mission, said all group members were in good health, but they were anxious to be allowed to go home soon.
"We have no indication when we will be sent home to our countries," Schneider told reporters as armed men in camouflage fatigues looked on. "We wish from the bottom of our hearts to go back to our nations as soon and as quickly as possible."
The group came to Slaviansk without weapons and were strictly in line with their mandate under OSCE rules, he added.
He said the military observers were "captured" Friday around 4 km outside the city as they were about to return to the regional hub city of Donetsk.
The OSCE said it has sent a negotiating team to the city trying to secure the entire team's release.
"We are doing everything we can," Natacha Rajakovic, a spokesperson of OSCE told Xinhua.
Slaviansk has become a flashpoint in the conflict between pro-Russia protesters and Ukrainian authorities in eastern Ukraine, where pro-Russia fighters have occupied a string of towns.
In a Saturday telephone conversation between U.S. Secretary of State John Kerry and Russian Foreign Minister Sergei Lavrov, the U.S. side called for Russia's help in releasing the European monitors while Lavrov urged the United States to assist in the release of the protest leaders arrested in southeastern Ukraine.
The captors said earlier Saturday that they have not ruled out releasing kidnapped Ukrainian army officials and international mediators in exchange for the release of their own men.
Washington and Moscow have been trading blame for the unrest in eastern Ukraine and the United States is preparing "a stronger position" to deter Russian President Vladimir Putin.
Conflicts have also been on the rise in the eastern city of Donetsk, where hundreds of pro-Russia protesters stormed and occupied a regional television station building Sunday afternoon.
The protesters broke the gate of the building and entered the regional television facility as about 30 policemen stood idly nearby and did not intervene.
Some 500 protesters gathered in front of the building, chanting slogans like "Russia!" and "Kiev cannot administer Donetsk!" and demanding the television station broadcast Russian TV programs, instead of Ukrainian ones.
Some people hoisted a flag of "the People's Republic of Donetsk" on the top of the building.
Earlier this month, pro-Russia protesters staged a rally to demand a referendum and some protesters complained that the television station did not give them a chance to speak.