The nationwide “anti-terrorist” operation announced by Ukraine’s security services (SBU) comes after government buildings were stormed by what are described as “extremist groups”.

The country’s security chief Oleksandr Yakymenko said sites had been attacked in several regions, and included military bases and arms depots.

The acting prime minister told a cabinet meeting he blamed “radicals” for the violence.

“It is unacceptable to talk about European values and the desire for a new level of Ukraine’s development and at the same time sacrifice human lives, destroy the state’s and citizens’ goods, burn their cars and apartments, and shame the country in the eyes of international community,” Serhiy Arbuzov said.

Earlier President Yanukovych said he held opposition leaders responsible after talks broke down.

Protesters have accused government agents of inciting the violence, by far the worst since the latest wave of demonstrations began three months ago.

The tug-of-war over whether Ukraine’s future direction lies west with Europe or east with Russia now seems to have become an open struggle for power.