KIEV (Reuters) - Armed separatists in the eastern Ukrainian city of Slaviansk seized a bus carrying international observers from the Organization for Security and Cooperation in Europe on Friday, the interior ministry said.

The group, which included 7 OSCE representatives and five members of the Ukrainian armed forces, was being held in the building of the state security agency (SBU) in the city which has been occupied by pro-Russian separatists.

"Negotiations are going on for their release," a ministry statement said.

(Reporting by Pavel Polityuk; Writing By Richard Balmforth)