A security officer and a pro-Russia activist were killed Sunday during a raid launched by Ukrainian special forces in the town of Sloviansk to take back government buildings occupied by pro-Moscow activists, a media report said.
"An anti-terrorist operation has begun in Sloviansk. It is being directed by the anti-terrorist centre of the state security service. Forces from all the security units of the country have been brought in," Interior Minister Arsen Avakov said on his Facebook page.
He said the men who seized the buildings opened fire at the approaching troops, killing one security officer and injuring five others, Xinhua reported.
"There are deaths and injuries on both sides. On our side, an SBU (Ukrainian Security Service) officer was killed and the head of the SBU's anti-terrorist centre has been wounded, as have four others. On the side of the separatists, an unidentified member was killed," Avakov was quoted as saying.
"Pass this on to all civilians, they should leave the centre of town, not come out of their apartments, and not go near the windows," Avakov announced to local residents to remain calm as special forces had begun to regroup.
Protestors also seized control of the mayor's office Sunday in Mariupol, another eastern Ukranian city.
A police station and a state security building were seized Saturday by armed men dressed in camouflage fatigues in Sloviansk, a town about 100 km north of regional capital Donetsk near the Russian border.
The armed men initially occupied the police station, where they seized at least 400 handguns and 20 automatic weapons.
"The aim of occupying the police station was the guns which they are giving out to the protestors in Sloviansk," an official said.
After seizing government buildings in Ukraine's eastern city of Donetsk, the protestors proclaimed the region's independence from Kiev last week.
Russia has refused to take responsibility for the protests in eastern Ukraine.