Ukraine prime minister Mykola Azarov says he sees "all the signs of a coup" as anti-government protests intensify in Kiev.
During a meeting with Western ambassadors on Monday, Mr Azarov said:
"This has all the signs of a coup ... That is very serious. We know that a plan is being prepared to seize the parliament.''
Demonstrators are blockading the main government building, as protests continuing against a decision not to sign a deal for closer ties with the European Union.
The headquarters of the cabinet is being blockaded and the BBC reports government employees are unable to reach work.
More protesters converged on Independence Square on Monday.
Ukrainska Pravda reported police reinforcements are being sent to Kiev, the capital.
Parliament is due on Tuesday to discuss the possible holding of a no-confidence vote in Mr Azarov's government.
President Viktor Yanukovych has urged police and demonstrators to observe the law.
"Any bad peace is better than a good war," he said in a TV interview.