Russia and the West locked horns over the escalating crisis in Ukraine at UN Security Council emergency talks Sunday as deadly clashes flared between Ukrainian forces and pro-Kremlin militias.

Russia pinned the blame on the pro-Western interim government in Kiev, which took power in February, as Britain, France and the United States pointed the finger at the Kremlin.

The emergency session was the 10th round of UN Security Council talks on the crisis and came after Kiev launched a military operation Sunday and gave pro-Russian forces a deadline of 0600 GMT Monday to give up their weapons to escape prosecution.

Russia, which called the meeting, said it was "the West who will determine the opportunity to stop the civil war in Ukraine" and alleged that Kiev was poised to unleash military action.

Ukraine sent special security forces into the city of Slavyansk on Sunday to regain control of a police station that had been seized by about 20 militants, resulting in dead and wounded on both sides, according to Ukraine's interior minister.

Ukrainian ambassador Yuriy Sergeyev accused Russia of sponsoring terrorism, posing a serious threat to the security of Ukrainians and to international peace and stability.

Russian ambassador Vitaly Churkin hit back that military operations in southeastern Ukraine would undermine talks between the European Union, Russia, Ukraine and the United States in Geneva this week.

Ukraine's acting president Oleksandr Turchynov declared the launch of a "full-scale anti-terrorist operation" a day after masked gunmen stormed police and security service buildings.

The attacks have been unsettling for both Kiev and Western leaders because of their similarity to events leading up to Russia's annexation of Ukraine's Crimean Peninsula.

Kiev's "provocation" would have "extremely significant consequences" for the people of Ukraine, Churkin warned.

'Dangerous escalation' of situation

The US ambassador said it was "hard to reconcile" the 40,000 Russian forces massed on the Ukrainian border and "subversive activities" inside Ukraine with Moscow's appeal for diplomacy.

"The credibility of the Russian Federation has been gravely undermined. That said we remain eager and willing to talk about how to de-escalate the situation," Samantha Power said.

"It will require the Russian Federation to pull back its forces which are ominously stationed and massed," she added.

Power accused Russia of waging propaganda and bombarding Ukraine with incitement and violence.

"This is the saddest kind of instability -- it is completely man made. This 'instability' was written and choreographed in and by Russia," she said.

British ambassador Mark Lyall Grant described the last 48 hours in eastern Ukraine as a "dangerous escalation of an already dangerous situation."

"Russia is seeking to impose its will on the people of Ukraine using misinformation, intimidation and aggression -- tactics drawn from the darkest days of the last century. This is completely unacceptable."

UN Assistant Secretary-General for Political Affairs Oscar Fernandez-Taranco said at least one Ukrainian officer had been killed in a gun battle and numerous other people had been reported injured during skirmishes in eastern Ukraine.

During the last 24 hours, he said, at least five new cities in the region had been targeted by uprisings and seizures of government buildings.

"The situation is therefore now more combustible than ever," Fernandez-Taranco said, warning against a spillover of "potentially severe consequences."