Heavily armed riot troops broke into the offices of a top Ukrainian opposition party office in Kiev tonight as anti-government protests crippled the capital for yet another day.
Elsewhere police dismantled or blocked off several small protest tent camps near key national government buildings in the city.
Tensions also rose as a double cordon of riot police deployed in the street near Kiev's city administration building, which demonstrators had occupied and turned into a makeshift command post and dormitory.
The moves came a day after hundreds of thousands of demonstrators crammed into Kiev, the biggest in three weeks of protests that started when Ukraine's president backed away from signing a long -awaited pact to deepen ties with the 28-nation European Union.
Protesters are angered not only by the thwarting of their desire to become closer to the West, but by police violence against the demonstrators.
Ostap Semerak, a member of the Fatherland Parry, said troops broke into the party's offices earlier tonight, some climbing in through its windows.
"They are storming us. The images are insane," he said by telephone.
The troops left after confiscating computer equipment, he said.
The party is headed by imprisoned former prime Yulia Tymoshenko, a longstanding foe of President Viktor Yanukovych, and is the largest opposition grouping in the parliament. Critics say Tymoshenko's conviction on abuse of office charges was a case of political revenge.
In a surprise move, Yanukovych announced he would sit down with three former Ukrainian presidents tomorrow to discuss a way out of the crisis that has paralysed the country. The European Union's foreign policy chief, Catherine Ashton, was also heading to the Ukraine to help defuse the tensions.
Ukraine's political standoff has been aggravated by its rapidly deteriorating finances. The economy has been in recession for more than a year, and the government is in desperate need of foreign funding to avoid a default. As talks stalled with the International Monetary Fund, Yanukovych has sought a bailout loan from Russia.
This former Soviet republic of 46 million people is sharply divided over the prospects of drawing closer to its powerful neighbour, Russia. Yanukovych's stronghold, is dominated by Russian speakers who want closer ties to Russia, in contrast to Kiev's students and residents in the west who see better EU ties as the way forward.
Opinion polls, however, show that the EU is more popular among Ukrainians than Russia.
Earlier Ukrainian police surrounded three tent encampments outside the government and presidential offices in central Kiev. Riot police also began removing barricades on the approach to the government building.
World boxing champion and opposition leader Vitali Klitschko warned the authorities against any further escalation in tensions.
"We are calling upon law enforcement to restrain from using force against peaceful demonstrators," he said as he tried to stop police from removing the tents.
A large protest test camp remained in place on Independence Square, the plaza that is the epicentre of the protests.
The square is a few hundred metres from the protester-occupied city administration building, which a court ordered demonstrators to leave by today. The appearance of riot police nearby raised anxieties inside, and some of the hundreds of people inside left.
Yesterday hundreds of thousands of protesters calling for Yanukovych's removal poured into Kiev, toppling a statue of former Soviet leader Vladimir Lenin and blockading government buildings.
Today they vandalised another Lenin statue in the southern town of Kotovsk.
"Only the legs are left standing," said town spokeswoman Yelena Khaustova.