KIEV (Reuters) - Ukraine's state security service said on Wednesday it was launching an "anti-terrorist operation" across the country after the seizure of administrative buildings and arms and ammunition depots by "extremist groups".

"In many regions of the country, municipal buildings, offices of the interior ministry, state security and the prosecutor general, army units and arms depots, are being seized," SBU chief Oleksandr Yakimenko said in a statement on the security service's website.

"Courtrooms are being burned down, vandals are destroying private apartments, killing peaceful citizens," he said.

The last 24 hours, he said, had shown "a growing escalation of violent confrontation and widespread use of weapons by extremist-oriented groups", he said.

The statement followed violent clashes between anti-government protesters and police in the capital Kiev on Tuesday in which at least 26 people were killed, including 10 police officers.

Reports from the regions of the sprawling country, particularly in the west, suggest groups backing the protest movement in Kiev have seized control of state buildings.

(Reporting By Richard Balmforth; Editing by Alastair Macdonald)