Interior Minister Arsen Avakov said in a Facebook post that a Security Service officer was killed in Slovyansk, where the police station and the Security Service office were seized a day earlier by camouflaged armed men. He also reported a number of casualties among the militia, but did not offer a number.
An Associated Press reporter found a bullet-ridden SUV on the side of the road and a pool of blood on the passenger seat where the gunbattle was supposed to have taken place.
Vladimir Kolodchenko, a lawmaker from the area who witnessed the attack, said a car with four gunmen pulled up on the road in a wooden area outside Slovyansk and open fire on Ukrainian soldiers who were standing beside their vehicles. Both attackers and the Ukrainian servicemen left soon after the shooting.
Unrest has spread to several municipalities in eastern Ukraine, including the major industrial city of Donetsk, which has a large Russian-speaking population.
Donetsk was also the support base for Viktor Yanukovych, the Ukrainian president ousted in February following months of protests in Kiev, the capital, that were ignited by his decision to back away from closer relations with the European Union and turn toward Russia. Ethnic Russians in Ukraine's east widely fear that the new pro-Western Ukrainian government will suppress them.
The regional administration in Donetsk issued a statement, confirming one dead and saying nine were wounded. It did not identify them, but said one person was shot outside Slovyansk.
Avakov has described the unrest as ``Russian aggression.''
Ukraine's foreign ministry issued a statement late Sunday afternoon accusing ``the Russian special service and saboteurs'' of fomenting unrest and pledged to present ``concrete evidence'' of Russia's involvement at next week's Ukraine summit in Geneva.
In an earlier post, he said the separatists who had seized the buildings in Slovyansk had opened fire on Ukrainian special forces sent to the city on Sunday. He called on residents to remain calm and stay at home.
An Associated Press reporter saw no signs of any shots fired at the police station, which was surrounded by a reinforced line of barricades. Unlike on Saturday, the men patrolling the barricades were largely unarmed. One of the guards who asked not to be identified denied reports of fighting at the police station.
Armed camouflaged men were guarding a checkpoint at the main entrance into the city.
Ukrainian lawmaker Oleh Lyashko said Sunday afternoon that Ukrainian forces managed to take control of the city hall, the Security Service's branch and the police station in Slovyansk. This could not be immediately verified.
In a phone call with Russian Foreign Minister Sergey Lavrov, U.S. Secretary of State John Kerry ``expressed strong concern'' that the attacks ``were orchestrated and synchronized, similar to previous attacks in eastern Ukraine and Crimea,'' according the State Department. Kerry ``made clear that if Russia didn't take steps to de-escalate in eastern Ukraine and move its troops back from Ukraine's border, there would be additional consequences,'' the department said.
The Russian Foreign Ministry denied Kerry's claims, while Lavrov blamed the crisis in Ukraine on the failure of the Ukrainian government ``to take into account the legitimate needs and interests of the Russian and Russian-speaking population,'' the ministry said. Lavrov also warned that Russia may pull out of next week's Ukraine summit if Kiev uses force against ``residents of the southeast who were driven to despair.''
Two rival rallies in another regional capital in eastern Ukraine, Kharkiv, turned violent. At the end of both rallies, a group of pro-Russian protesters followed several pro-Ukrainian activists, beating them with bats and sticks, Interfax Ukraine reported. A video on Espresso TV showed one activist with blood on his head and hands waiting for paramedics on the steps of the underground passage. Several men and women came up to him and started kicking him.
Interfax quoted Kharkiv authorities saying that 10 people were injured at the rallies.
In Slovyansk, the mayor said Saturday the men who seized the police station were demanding a referendum on autonomy and possible annexation by Russia. Protesters in other eastern cities have made similar demands after a referendum in Crimea last month in which voters opted to split off from Ukraine, leading to annexation by Russia.
Overnight, the interior minister reported an attack on a police station in the nearby city of Kramatorsk. A video from local news website Kramatorsk.info showed a group of camouflaged men armed with automatic weapons storming the building. The news website also reported that supporters of the separatist Donetsk People's Republic have occupied the administration building, built a barricade with tires around it and put a Russian flag nearby.
Regional news website OstroV said three key administrative buildings have been seized in another city in the area, Enakiyeve. In Mariupol, a city south of Donetesk on the Azov Sea and just 50 kilometers (30 miles) away from the Russian border, the city hall was seized by armed masked men. Local news website 0629.com.ua said 1,000 protesters were building a barricade around it while unknown armed men raised the Russian flag over the building.
On Saturday in Donetsk, the regional capital, witnesses said the men who entered the police building were wearing the uniforms of the Berkut, the feared riot police squad that was disbanded in February after Yanukovych's ouster. Berkut officers' violent dispersal of a demonstration in Kiev in November set off the mass protests that culminated in bloodshed in February when more than 100 people died in sniper fire. The acting government says the snipers were police.