SLOVYANSK, Ukraine -- Ukraine is launching a "large-scale anti-terrorist operation" to resist attacks of armed pro-Russian forces, Ukraine's President Oleksandr Turchynov said on Sunday in a televised address.
The authorities in Kiev will use the army in order to prevent Russian forces from moving in, as they did in Crimea, Turchynov said, pledging amnesty to anyone laying down arms by Monday morning.
"The Security Council has made a decision to begin a large-scale anti-terrorist operation with participation of army forces," he said. "We're not going to allow Russia to repeat the Crimean scenario in Ukraine's east."
While there has been no formal response from Russia yet, that country's foreign ministry announced late Sunday it wanted the Ukraine crisis urgently put on the U.N. Security Council's agenda, Reuters reports.
Ukraine's central government has repeatedly blamed its problems in in the escalating crisis on an increasingly aggressive Kremlin.
"The blood of Ukrainian heroes has been shed in a war which the Russian Federation is waging against Ukraine," Turchynov said in an address to the nation, according to Reuters. "The aggressor has not stopped and is continuing to sow disorder in the east of the country."
NATO described the appearance in eastern Ukraine of men with specialized Russian weapons and identical uniforms without insignia - as previously worn by Moscow's troops when they seized Crimea - as a "grave development," Reuters reports.
The White House has repeatedly condemned Russia's behavior in the Ukraine.
U.S. Secretary of State John Kerry "expressed strong concern" that the recent attacks in the east "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.
On Sunday, Sen. John McCain, R-Ariz., said on CBS' "Face the Nation" the rising unrest is the result of U.S. failure to "enact anything really meaningful and important as a result of [Russian President] Vladimir Putin's incursion and annexation under Crimea, which was predictable. And what he's doing now is predictable."
McCain called on the Obama administration to provide more small arms to Ukraine's central government, as well as intelligence sharing, adding that Kiev feels abandoned by Washington.
Ukrainian special forces exchanged gunfire with a pro-Russia militia in an eastern city Sunday morning, with at least one security officer killed and five others wounded. It was the first reported gunbattle in eastern Ukraine, where armed pro-Russia men have seized a number of government buildings in recent days.
Turchynov said a Security Service captain was killed and two colonels wounded in a gunbattle outside Slovyansk, where the police station and the Security Service office were seized a day earlier.
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.
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.