KIEV, Ukraine — The Ukrainian authorities’ surprise decision to storm the central square occupied by antigovernment protesters here early Wednesday sharply escalated tensions with Western leaders, while an equally abrupt pullout by the police after a nine-hour siege created a growing sense of unpredictability about President Viktor F. Yanukovich’s handling of the crisis.

The strange enforcement action, which antagonized and energized demonstrators but did not clear them from the square, added to the problems of Ukraine’s economy. The country was already facing a severe cash shortage but in recent days has seen its borrowing costs rise to record highs, with the central bank forced to intervene to support the currency.

Mobilizing after midnight, thousands of riot police officers and Interior Ministry troops broke through barricades around Independence Square, pushed demonstrators back and formed tight cordons around them. They then called in bulldozers and other heavy equipment to raze some of the protesters’ tents and barricades.

The security forces clashed with protesters and briefly tried to regain control of City Hall. Then at 10:30 a.m., they abruptly withdrew, raising new questions about Mr. Yanukovich’s handling of the crisis, which has seemed increasingly erratic. The retreat let protesters reclaim the square and they quickly rebuilt their barriers, this time using heaping bags of snow.