Pro-Russian separatists in eastern Ukraine have seized a bus carrying international military observers, Ukraine’s interior ministry says.
Negotiations were under way to secure the release of the observers, seized near the town of Sloviansk, it added.
Western leaders earlier announced they were debating fresh sanctions against Russia over its alleged failure to help de-escalate the crisis in Ukraine.
Russia has accused the West of wanting to “seize” Ukraine.
Moscow has tens of thousands of troops stationed along its side of the border with Ukraine and pro-Russian separatists have been occupying key buildings in a dozen eastern towns, defying the central government in Kiev.