Turning to force to try to restore its authority in the vital industrial east, Ukraine's government announced Sunday it was sending in troops to try to quash an increasingly brazen pro-Russian insurgency, despite repeated warnings from the Kremlin.

Accusing Moscow of fomenting the unrest, Ukrainian President Oleksandr Turchynov said in a televised address that such a "large-scale anti-terrorist operation" would ensure Russia did not "repeat the Crimean scenario in Ukraine's east." Turchynov pledged to offer amnesty to anyone surrendering their weapons by Monday morning.

Reliance on the military is a response that hints at concerns over the reliability of the police, who have often proven unable or unwilling to repel pro-Russian gunmen and other Moscow loyalists from seizing key state facilities. With tens of thousands of Russian troops massed along Ukraine's eastern border, there are fears that Moscow might use unrest in the mainly Russian-speaking region as a pretext for an invasion.

These are not protests, these are professional military operations. - U.S. Ambassador Samantha Power

Speaking late Sunday on Russian state television, ousted president Viktor Yanukovych accused the CIA of being behind the new government's decision to turn to force, a claim the CIA denied as "completely false."

Yanukovych claimed that CIA director John Brennan met with Ukraine's new leadership and "in fact sanctioned the use of weapons and provoked bloodshed."

CIA spokesman Dean Boyd said that while the agency doesn't comment on Brennan's travel itinerary, the "claim that director Brennan encouraged Ukrainian authorities to conduct tactical operations inside Ukraine is completely false."

UN Security Council holds emergency session

Ukraine now has "one foot into a civil war," Yanukovych declared, flanked by his former prosecutor general and interior minister, the two associates most despised by the protesters whose months-long demonstrations were ignited by Yanukovych's decision to back away from closer relations with the European Union and turn toward Russia. Yanukovych fled to Russia in February, saying he feared for his life.

Tensions are on the rise in eastern Ukraine as armed militants carried out a series of seizures of police stations and government buildings in the region. Kyiv has called the events, eerily reminiscent of what occurred in Crimea before it was annexed by Russia last month, intentional 'acts of aggression.' (Maxim Dondyuk/The Associated Press)

Earlier Sunday, Ukrainian special forces exchanged gunfire with a pro-Russia militia outside the eastern city of Slovyansk — the first reported gun battle in the east, where armed pro-Russian men have seized a number of key government buildings to press their demands for referendums on autonomy and possible annexation by Russia, following the pattern set by the vote in Crimea last month. A Ukrainian security officer was killed and at least two others wounded.

Calling such attacks a "Russian aggression," Interior Minister Arsen Avakov said in a Facebook post Sunday that special forces of up to 12,000 people will be drawn from volunteers who will be tasked with resisting attacks from pro-Russian forces in their local areas.

Russia's Foreign Ministry was quick to dismiss Turchynov's decree as "criminal" and accused Ukrainian officials of using radical neo-Nazi forces.

In an emergency session of the UN Security Council late Sunday, Russian Ambassador Vitaly Churkin denied claims that Moscow was behind the violence.

"It is the West that will determine the opportunity to avoid civil war in Ukraine. Some people, including in this chamber, do not want to see the real reasons for what is happening in Ukraine and are constantly seeing the hand of Moscow in what is going on," Churkin said.

In response, U.S. Ambassador Samantha Power said, "These are not protests, these are professional military operations."

Unrest has spread to several municipalities in eastern Ukraine, including the major industrial city of Donetsk, which has a large Russian-speaking population and was the support base for Yanukovych. Ethnic Russians in Ukraine's east widely fear that the new pro-Western Ukrainian government will suppress them.

Several town halls and other government buildings were occupied by crowds of supporters of the referendum drive to give eastern regions wide powers of autonomy.

2 Slovynask buildings seized

A police station and the local security services headquarters in Slovyansk, some 150 kilometres west of the Russian border, were the latest to fall to storming Saturday by well-armed and effectively co-ordinated militia. Both were still in the hands of gunmen Sunday, despite a government drive to retake them.

The police station was surrounded by a reinforced line of barricades, but there was a less noticeable presence of the automatic rifle-toting pro-Russian gunmen of the day before. Hundreds of residents beyond the barricades sang songs and shouted in support of the men seizing the building.

At least one Ukrainian security officer has been killed after fire-fights with pro-Russian separatists that took control of the police headquarters and a security building in the eastern city of Slaviansk on Sunday. (Gleb Garanich/Reuters)

The only confirmed casualties in Slovyansk were among Ukrainian government forces.

Turchynov said a Security Service captain was killed and two colonels were wounded in Sunday's gun battle. An Associated Press reporter saw a bullet-ridden SUV on the side of the road and a pool of blood by the front passenger seat door, where the clash was reported to have occurred.

Turchynov said pro-Russia militiamen were responsible for the attack.

Vladimir Kolodchenko, a lawmaker from the area who said he witnessed the attack, said a car carrying four gunmen pulled up by a wooded area where government troops were standing by several parked armoured personnel carriers and other vehicles.

Kolodchenko, who expressed sympathy for the pro-Russian groups, described the attack as a provocation and an attempt to create a pretext for an all-out assault on Slovyansk.

More referendums called for

Those leading the storming of government buildings say Russian-speakers rights can only be assured with full autonomy for eastern regions — a move they insist should be endorsed by referendums. A similar vote in Crimea last month resulted in the peninsula splitting off from Ukraine and being annexed by Russia.

In Luhansk — a town of 420,000 across the border from Russia — heavily armed men still control the security services building. In Donetsk, about 129 kilometres to the west, an occupied regional government building is now serving as the headquarters of a self-declared autonomous region billing itself the Donetsk Republic.

All occupations have drawn crowds of sympathizers.

Ukraine's Foreign Ministry issued a statement late Sunday afternoon accusing "the Russian special service and saboteurs" of fomenting unrest and pledging to present "concrete evidence" of Russia's involvement at a summit on Ukraine in Geneva on Thursday.

In a phone call with Russian Foreign Minister Sergey Lavrov late Saturday, 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.

The Russian Foreign Ministry denied Kerry's claims, saying Lavrov blamed the crisis in Ukraine on the failure of the Kyiv government "to take into account the legitimate needs and interests of the Russian and Russian-speaking population." Lavrov also warned that Russia may pull out of the Ukraine summit if Kyiv 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 on Sunday when a group of pro-Russian protesters followed several pro-Ukrainian activists, beating them with bats and sticks, Interfax Ukraine news agency reported. Interfax quoted Kharkiv authorities as saying 10 people were injured at the rallies.

An attack was also reported 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 website also reported that supporters of the separatist Donetsk Republic occupied the administration building, built a barricade with tires around it and planted a Russian flag nearby.

Regional news website OstroV said three key administrative buildings were seized in another city in the area, Enakiyeve. In Mariupol, a city on the Azov Sea just 30 miles 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 armed men raised the Russian flag over the building.