An armed man looks on in front of the police headquarters in Slaviansk, April 12, 2014. [Photo/Agencies]

Ukraine crisis

DONETSK -- About a dozen gunmen seized a police station in eastern Ukraine Saturday amid simmering tensions in the country's Russian-speaking regions.

The incident took place early morning in Slavyansk, a town about 100 km north of regional capital Donetsk, where pro-Russian protesters occupied a government building nearly a week ago.

Ukraine Interior Minister Arsen Avakov said on his Facebook account the attack was led by "armed men in camouflage fatigues" and he vowed a severe response.

Ukrainian special forces had been dispatched to the scene, Avakov said, adding there was zero tolerance for armed terrorists.

Casualties and hostages remain unknown.

Meanwhile, Donetsk separatist leader Sergiy Tsyplakov claimed responsibility for the raid in a statement issued to Russia's state-run RIA Novosti news agency, but insisted his people were not armed.

A new wave of unrest erupted in Ukraine last weekend, when pro-Moscow activists seized several government buildings in the eastern cities of Donetsk, Lugansk and Kharkov, demanding a referendum on autonomy and closer ties with Russia.

On March 18, Russian President Vladimir Putin and Crimean leaders signed a treaty to make the southern peninsula part of Russian territory after almost 97 percent of Crimean voters backed secession from Ukraine in a referendum.

Kiev has rejected the referendum and Crimea's integration into Russia, saying it was unconstitutional.