Pro-Russian armed men seized control of parliament and government buildings in the Ukrainian region of Crimea on Thursday and hoisted Russian flags, officials said.
Up to 50 men with weapons marched into the buildings in the regional capital of Simferopol in a dawn raid and blocked government workers from entering, Crimean prime minister Anatoliy Mohilyov said.
Local authorities were preparing to "take measures", Mohilyov said without elaborating.
Ukraine's interim interior minister Arsen Avakov said security forces were being mobilised. "Interior troops and the entire police force have been put on alert," Avakov said in a statement on Facebook, adding that the area had been cordoned off "to prevent bloodshed".
In a statement the regional government asked employees "not to come to work today."
An AFP journalist at the scene said police were pushing people back from around occupied administrative buildings.
Dozens of men in full combat dress but without any markings of affiliation marched into the government and parliament and removed the guards without any fight, the Interfax-Ukraine news agency quoted sources in parliament as saying. It said they gained entrance to the building complex by firing on the glass doors but that no-one was hurt.
Meanwhile, unconfirmed reports said a large number of cars were seen travelling from the pro-Russian port town of Sevastopol towards Simferopol.
The moves came amid concerns of growing separatism on the overwhelmingly pro-Russian peninsula on the Black Sea after the ousting of pro-Moscow president Viktor Yanukovych.
The head of the local assembly for Crimea's Muslim Tatar minority – which is fearful of any pro-Russian separatist moves – confirmed that the buildings had been seized. "I was told that the buildings of the Crimean Verkhovna Rada (parliament) and the Crimean Council of Ministers (government) are occupied by armed men in uniform without identification signs," Refat Chubarov wrote on Facebook. "They have not put forward any demands yet."
Unconfirmed news reports said the buildings were being controlled by Russian-speaking militia groups formed by the local population.
Many in Crimea, which is overwhelmingly Russian rather than Ukrainian speaking, strongly oppose the takeover of Ukraine by pro-EU and anti-Kremlin forces.