Ukraine’s security forces have been put on alert after government buildings in the Russian-majority Crimea region were seized by armed men.
The Russian flag had been raised over both buildings in the capital, Simferopol.
The local government has said it is negotiating with the gunmen.
The seizure of the buildings comes a day after confrontations between pro-Russian separatists and supporters of Ukraine’s new leaders.
The incident is another illustration of tensions in the region, the BBC’s Mark Lowen reports from Crimea.
On Wednesday Simferopol saw clashes erupt between Ukrainians who support the change of government and pro-Russians.
Ukrainian Interior Minister Arsen Avakov said the area near the government buildings has been cordoned off to prevent “bloodshed”. He added that the seizure of the buildings was the work of “provocateurs”.
“Measures have been taken to counter extremist actions and not allow the situation to escalate into an armed confrontation in the centre of the city,” he said in a statement on his Facebook page.
Regional Prime Minister Anatoliy Mohylyov told a local TV station said he would take part in talks with the gunmen and told government employees who normally work there not to come in.
The men have not yet made any demands or issued any statements but did put up a sign reading: “Crimea is Russia”.
They threw a flash grenade in response to questions from a journalist, AP news agency reported.
Tensions have been rising in Crimea since President Viktor Yanukovych was ousted last week.
Crimea – where ethnic Russians are in a majority – was transferred from Russia to Ukraine in 1954.
Ethnic Ukrainians loyal to Kiev and Muslim Tatars – whose animus towards Russia stretches back to Stalin’s deportations during World War II – have formed an alliance to oppose any move back towards Moscow.
On Wednesday Prime Minister designate Arseniy Yatsenyuk said: “In Crimea we always had different sentiments and forces who try to split the country and proclaim separatism.”
But he told the BBC that Ukraine “could cope”.
Crimea was transferred from Russia to Ukraine in 1954.
Russia, along with the US, UK and France, pledged to uphold the territorial integrity of Ukraine in a memorandum signed in 1994.