KIEV - The Ukrainian government on Sunday launched an "anti-terrorist" operation in an eastern city where armed pro-Russian men seized police and security services buildings, Interior Minister Arsen Avakov said.

"An anti-terrorist operation has begun in Slavyansk. It is being directed by the anti-terrorist center of the state security service. Forces from all the security units of the country have been brought in," Avakov was quoted by the Interfax news agency as saying on his Facebook page.

He said the men who seized the buildings opened fire on the approaching troops, adding that both sides had suffered casualties during the raid.

"There are deaths and injuries on both sides. On our side -- an SBU (Ukrainian Security Service) officer. The head of the SBU's anti-terrorist center has been wounded, as have four others," he said. "On the side of the separatists -- an unidentified number."

Avakov said the special forces had begun to "regroup" and urged local residents to remain calm and stay at home as a safety precaution.

"Pass this on to all civilians: they should leave the center of town, not come out of their apartments, and not go near the windows," he said.

The Ukrainian government's move came one day after about a dozen gunmen seized a police headquarters and the Security Service office in Slavyansk amid simmering tensions in the country's Russian-speaking regions.

A new wave of unrest erupted in Ukraine's east last weekend, when pro-Moscow activists seized several government buildings in the 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 with Russia, saying it was unconstitutional.

Ukraine moves to end separatist grip on eastern town	Gunmen seize building in eastern Ukraine