At least a dozen armed men have seized a police station in a small town in eastern Ukraine as tensions in the country's Russian-speaking regions intensify.
The Interior Ministry said men in camouflage stormed a police station in Slovyansk, 55 miles south of regional centre Donetsk, where pro-Russian protesters have occupied a government building for nearly a week.
Interior minister Arsen Avakov pledged a "very tough response" to the seizure.
Video on a local website showed several armed men in balaclavas guarding the entrance to the police station.
Protesters who have held the administration building in Donetsk since Sunday initially called for a referendum on secession but later reduced the demand to a vote on autonomy within Ukraine.
Prime Minister Arseniy Yatsenyuk told leaders in the east of the country that he was committed to allowing regions to have more powers.
He told reporters he favoured a peaceful solution to the stand-off with Russia, but left it unclear how his ideas differ from the demands of protesters occupying government buildings in the east or from Moscow's advocacy of federalisation.
He also left the door open to storming the buildings occupied by armed men, even though a two-day deadline announced earlier this week has passed.
The officials who met Mr Yatsenyuk in Donetsk did not include representatives of the protesters. They asked Mr Yatsenyuk to allow referenda on autonomy for their regions, but not on secession.
"There are no separatists among us," said Gennady Kernes, mayor of Kharkiv, Ukraine's second-largest city, where protesters occupied a government building earlier in the week.
Ukraine's eastern industrial heartland was the support base for Kremlin-friendly president Viktor Yanukovych, who was ousted in February after months of protests. Last month, the Crimea region voted to secede and was annexed by Russia.
Moscow ratcheted up the pressure on Ukraine yesterday when president Vladimir Putin warned European leaders of a risk to the gas supplies going through Ukraine. He has threatened that Russia could shut off shipments to Ukraine if it fails to pay its mammoth debts.
Mr Putin's spokesman Dmitry Peskov told Russian news agencies that Moscow has not heard from the countries to which Mr Putin sent a letter.
Protesters in the eastern cities of Donetsk and Luhansk occupied government buildings and called for referenda on regional autonomy that could prefigure seeking annexation by Russia.
Mr Yatsenyuk said the grievances of eastern Ukraine would be appeased by the upcoming constitutional reform that will "satisfy people who want to see more powers given to regions". He mentioned abolishing Kiev-controlled local administration as one of the steps to decentralise the country.
The men who stormed the police station have not presented any demands, the Interior Ministry said.
Local media reported that special forces troops had been dispatched to the area.
Videos showed several men armed with machine guns in balaclavas guarding the entrance to the police station. They were wearing St George's ribbons, a symbol of the Soviet Union's victory in the Second World War, which has become a symbol of pro-Russian protesters in eastern Ukraine.
Gunshots rang out in a video from the scene after an armed man shouted to a cameraman to stop recording. No casualties were immediately reported.
The town's mayor, Nelya Shtepa, said on local television that she was holding talks with the attackers who she insisted were from the area.