Crimea's regional government building and parliament have reportedly been taken over by armed men, further loosening the grip of Ukraine's new government on the Russian-speaking east of the country.
News of the takeover was carried by Russian news agency Interfax, citing a Facebook post by a Tatar leader which claimed key government buildings in the capital, Simferopol, were seized by men in uniform whose identity could not be established.
"I have been told that the buildings of parliament and the council of ministers have been occupied by armed men in uniforms that do not bear any recognisable insignia.... They have not yet made any demands," Tatar leader Refat Chubarov posted on Facebook.
Meanwhile Reuters claims its correspondent at the scene saw Russian flags flying over both the regional government headquarters and the parliament.
Local people said they had heard gunfire in the night and saw a lot of people going into the building.
Earlier reports suggested pro-Russian fighters had set up checkpoints on the road linking Sevastopol Simferopol, as they moved from their Black Sea port base.
At least a dozen men in fatigues were seen under a Russian flag around the halfway mark on the 80-kilometre road from Sevastopol to Simferopol, and they were supported by an armoured personnel carrier, the Globe and Mail reported.
The removal of pro-Russian Ukraine President Viktor Yanukovich after prolonged anti-government protests in Kiev triggered a backlash in the Russian-speaking regions in the east of the country, with widespread clashes between thousands of Muslim Tatars and pro-Russian demonstrators in Simferopol.
Russian president Vladimir Putin has ordered the military to be on war alert. However the Kremlin has denied its military drills are linked to the Ukraine crisis and Moscow's territorial claims in Crimea.
The United States has reacted strongly, saying Russian military intervention in Crimea will violate the sovereign territorial integrity of Ukraine. US Secretary of State John Kerry warned Russia that armed intervention in the Crimea would be a "grave mistake".
Meanwhile, in Kiev, the leaders of the popular protest that overthrew Yanukovich have pressed ahead with efforts to set up an interim government, which would facilitate talks with the International Monetary Fund over a financial aid package for the country whose currency nosedived to 10-year lows following the upheaval.
Ukraine's former economy minister Arseny Yatseniuk was chosen by the "Euromaidan council" to lead the incoming interim government. The council also named key ministers in the new government, and Oleksander Turchinov, the acting president, said the government will have to take several unpopular measures in the coming days.
"This is a government which is doomed to be able to work only for 3-4 months ... because they will have to take unpopular decisions," Turchinov said, according to Reuters.