In the Ukrainian city of Slaviansk, where pro-Russian separatists are holding a group of international observers, the self-declared "people's mayor" says he's willing to let them go -- but with a price.

(SOUNDBITE) (Russian) SEPARATIST LEADER VYACHESLAV PONOMARYOV, SAYING:

"The Kiev junta has our fellows and comrades. Therefore, if there is a possibility, we are ready for an exchange."

He told a news conference capturing the observers for a swap was not a preconceived plan.

(SOUNDBITE) (Russian) SEPARATIST LEADER VYACHESLAV PONOMARYOV, SAYING:

"That was not our plan (to take prisoners for a swap). But you understand that prisoners have always been coins to exchange during times of war. It's an international practice to swap prisoners. There is nothing scary about it."

German Foreign Minister Frank-Walter Steinmeier says the detained group includes four Germans.

(SOUNDBITE) (German) GERMAN FOREIGN MINISTER, FRANK-WALTER STEINMEIER, SAYING: