SLAVYANSK, Ukraine - The UN Security Council held emergency talks Sunday after Ukraine declared a "full-scale" military operation against pro-Russia forces, amid deadly clashes in its restive east.
Russia and the West locked horns over the escalating crisis in Ukraine with Russian ambassador Vitaly Churkin saying "there has already been bloodshed and a further escalation must be swiftly stopped".
US ambassador Samantha 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. It was written and choreographed in and by Russia," Power told the 15-member council.
The latest clashes broke out a day after masked gunmen stormed police and security service buildings in coordinated raids, especially unsettling for Kiev and Western leaders because of their similarity to events leading up to Russia's annexation of Ukraine's Crimean Peninsula.
Ukraine's Interior Minister Arsen Avakov announced the launch of a counterstrike against the armed separatists in the eastern Donetsk region early on Sunday morning.
"There are dead and wounded on both sides. On our side - an SBU officer. The head of the SBU's anti-terrorist centre has been wounded, as have four others," Avakov wrote on his Facebook page.
"On side of the separatists - an unidentified number. The separatists have started to protect themselves using human shields."
Ukraine's acting President Oleksandr Turchynov later declared the launch of a "full-scale anti-terrorist operation".
Turchynov told the nation in a televised address that "we will not allow Russia to repeat the Crimean scenario in the east of Ukraine".
"Blood has been spilt in a war that is being waged against Ukraine by Russia," said Turchynov.
"The national security and defence council has decided to launch a full-scale anti-terrorist operation involving the armed forces of Ukraine," he announced Kiev gave the pro-Russian forces a deadline of 0600 GMT Monday to give up their weapons to escape prosecution.
The Russian foreign ministry immediately responded by accusing Ukraine's leaders of "waging war against their own people".
US ambassador Power urged Russia to explain why 40,000 of its forces are massed on the Ukrainian border and find constructive ideas to stop armed attacks on government buildings in eastern Ukraine.
'Ongoing armed standoff'
Moscow has denied playing a role in the latest wave of violence and previously told Kiev that its armed response could ruin the chances of the two sides sitting down for US-EU mediated talks in Geneva on Thursday.
The heavily Russified region has been riven by unrest since pro-Western leaders rose to power in February on the back of bloody protests against the old regime's decision to reject an EU alliance and turn towards Moscow.
Russia has also threatened to halt its neighbour's gas supplies over unpaid bills - a cutoff that would impact at least 18 EU nations.
European Union foreign ministers will hold talks in Luxembourg Monday dedicated to the growing Ukraine crisis and the threat of a cut in Russian gas deliveries.
Avakov said crack units from Ukraine's SBU security service moved Sunday into the city of Slavyansk to regain control of a police station that had been seized by about 20 militants on Saturday.