Ukraine's acting president has pledged "anti-terrorist measures" after pro-Russian protesters declared the region of Donetsk an independent republic and clashes erupted in two other eastern cities.
In a televised appeal on Monday, Oleksandr Turchynov said that the action in Kharkiv, Donetsk and Luhansk showed that Russia was "playing out the Crimean scenario" - a reference to the Russian takeover and annexation of the peninsula.
"We will not allow this," he said. Warning that some activists had taken up arms, Turchinov said: "Anti-terrorist measures will be carried out against those who had taken up weapons."
Earlier on Monday, pro-Russian protesters occupying a regional administration building in Donetsk declared the creation of a "people's republic" separate from Ukraine.
"In the event of aggressive action from the illegitimate Kiev authorities, we will appeal to the Russian Federation to bring in a peacekeeping contingent," said the proclamation, voiced by an unidentified man.
The activists later read out the text to a cheering crowd of about 1,000 people outside the building.
"An anti-Ukrainian plan is being put into operation ... under which foreign troops will cross the border and seize the territory of the country," said Arseniy Yatsenyuk, Ukraine's acting prime minister. "We will not allow this."
Demand of referendums
After seizing official buildings in Kharkiv, Luhansk and Donetsk on Sunday night, pro-Russian activists demanded that referendums be held on whether to join Russia.
The interior minister, Arsen Avakov, said on Monday that the main regional administration building in Kharkiv had been cleared of "separatists", but not before clashes in front of the building in which nine people were injured.
Police in Luhansk said protesters occupying the state security building there had seized weapons.
Avakov on Sunday accused the Russian president, Vladimir Putin, of orchestrating the "separatist disorder" and promised that disturbances would be brought under control without violence.
Late on Monday, the Russian foreign ministry issued said the Ukraine government should stop blaming Russia for its problems.
"If irresponsible treatment of one's country, one's nation, by the political forces who call themselves the Ukrainian authorities continues, Ukraine will inevitably be facing new troubles and crises," it said.
Russia has been pushing a plan of a federal Ukraine, in which regions of the country of 46 million would have broad powers of autonomy.
Ukraine, which is drawing up its own plan for "de-centralisation" linked to regional development, said Russia aimed to break up the country.