Ukraine has launched its first major offensive against the insurgency sweeping the east of the country, killing and wounding a number of militants.

Police have cleared a city hall in south-eastern Ukraine of pro-Russian protesters who had been occupying it for more than a week, Ukrainian Interior Minister Arsen Avakov said today.

Three pro-Russian militants have been killed and 13 wounded after Ukrainian troops repelled an attack on a National Guard base in the Black Sea port of Mariupol in the south east of the country.

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.

Pro-Russia demonstrators who seized the regional administration building in Ukraine’s second-largest city have been driven out of the building and about 70 of them were arrested, Ukraine’s interior minister said today.

Ukraine accused Russia’s president, Vladimir Putin, of orchestrating the seizure of state buildings in two eastern Ukrainian cities by pro-Russia protesters yesterday, in a further escalation of tension between Kiev and Moscow.

Russia sharply hiked the price for natural gas to Ukraine today, raising the heat on its cash-strapped government, while Ukrainian police moved to disarm members of a radical nationalist group after a shooting spree in the capital, Kiev.

Barack Obama has warned Moscow “there will be costs” if Russia intervenes militarily in crisis-torn Ukraine.

Russian forces have been accused of “an armed invasion” after units blocked a Ukrainian military airport in the Black Sea port of Sevastopol in Crimea.

Ukraine’s acting interior minister says troops and police have been put on high alert after dozens of men seized local government and legislature buildings in the Crimea region.

Fighting broke out between pro and anti-Russian demonstrators in Ukraine’s Crimea region as Russian president Vladimir Putin ordered military exercises just across the border.

Ukraine issued an arrest warrant yesterday for its ousted pro-Russian president over “mass murder” and appealed for $35bn (€25bn) in Western aid as Moscow denounced Kiev’s new reformist interim government as “Kalashnikov-toting people in black masks.”