Armed men have seized a police station and a security services building in eastern Ukraine, officials say. Police said the men fired shots and used stun grenades to seize the offices in Sloviansk, near the Russian border.
The interior minister called the gunmen "terrorists" and said special forces would repel the attack.
Pro-Russian activists have seized government buildings elsewhere in east Ukraine. Kiev accuses Moscow of orchestrating the unrest.
Interim Foreign Minister Andrei Deshchytsia urged Moscow to end "provocative" actions by its agents. Eastern Ukraine has a large Russian-speaking population and has seen a series of protests since the ousting of President Viktor Yanukovych in February.
Protesters in largely Russian-speaking Donetsk, 130km (80 miles) from Sloviansk, have been occupying government buildings for days and demanding a referendum on becoming part of Russia.