Clashes between pro-government and anti-government protestors Friday in Ukraine's Black Sea city of Odessa have killed at least 43 people and injured 174, the government said.
Among the dead, mostly pro-Russia protestors, 30 were choked to death when radicals set fire on a trade union building, while eight others died from jumping out of windows of the burning building, Xinhua reported Saturday.
Up to 50 people, including 10 policemen, have sought medical assistance after the clashes between the Right Sector, a Ukrainian ultra-nationalist group, and pro-Russia militants.
The municipal government has declared three days of mourning in Odessa.
Police told Russia's ITAR-TASS news agency that riots erupted earlier between football fans from the eastern city of Kharkov and Right Sector radicals who had come from Kiev.
Ukraine's defence ministry has confirmed the loss of two helicopters. It said the aircraft were shot down by surface-to-air missiles, which it said proved the activists were not civilians but well-equipped and well-trained militants.
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Russia said the military operation in Sloviansk meant Kiev had "crossed out" the Geneva agreements reached April 17.
Calling the military move a "manifestation of a crime of feebleness of Kiev authorities", Russian Prime Minister Dmitry Medvedev urged those in power to "come to their sense...otherwise the country's fate might be completely sad".