Around 40 people have been held captive in Ukraine's eastern town of Sloviansk, where pro-Russia protestors seized government buildings, authorities said Monday.
According to Maryna Ostapenko, spokesperson of the Ukrainian Security Service (SBU), the activists who have captured the people, have not put forward any demand to release the hostages, Xinhua reported.
Ostapenko said Russian Special Forces "might be involved" in the kidnapping of European military observers in the eastern city of Sloviansk.
Pro-Russian activists seized a bus last week with eight international observers, who were operating under the mandate of the Organisation for Security and Cooperation in Europe (OSCE).
The captors claimed to have found a Ukrainian spy travelling with the group.
The activists freed one of the observers Sunday for health reasons, but said they had no plans to release the others.
The pro-Russian protestors Monday seized another government building in Gorlovka in Donetsk region.