Crimea crisis and unrest in eastern Ukrainian cities
Armed men in masks, representing Ukrainian special forces, stand guard outside the regional administration building in KharkovReuters

Ukraine has begun anti-terror operations in its eastern cities including Kharkov arresting at least 70 pro-Russian protesters to bring the situation under control.

Ukrainian forces raided the building of the regional administration in Kharkov which was earlier stormed by the protesters.

"To date, the building of the regional state administration is guarded by law enforcement officers and servicemen of the armed forces of Ukraine and is completely ready for work," said Ihor Baluta, the regional chief of the eastern Ukrainian city, who was recently appointed by the Kiev administration.

No weapons are reported to have been used during the counter-terror measures but minor skirmishes have broken out injuring a few people.

Ukraine's interior minister Arsen Avakov said in his Facebook post: "Counterterrorism operation in Kharkov has begun, city's downtown is blocked. So are the metro stations. There is nothing to worry about. Kharkov Regional State Administration building is clear from protesters. Firearms were not used during the operation."

Ukraine's special forces have been scrambled across the eastern and southern regions of the country following the unrest which began over the weekend when pro-Russian protesters stormed the state buildings demanding a referendum.

Meanwhile, the US has warned Russia not to interfere in Ukrainian affairs.

Speaking to his Russian counterpart Sergei Lavrov over telephone, US Secretary of State John Kerry said Moscow would "incur costs" if it presses ahead with its activities in destabilising Ukraine.

According to State Department spokesperson Jen Psaki, Kerry "made clear that any further Russian efforts to destabilise Ukraine will incur further costs for Russia".

Kerry insisted the latest developments in Ukraine "do not appear to be a spontaneous set of events".