The European Union's top diplomat Catherine Ashton was set to hold emergency talks in Ukraine on Tuesday amid growing international concern at the crisis that has pitted the security forces against pro-EU demonstrators.
At least 10 protesters were reported injured in fresh clashes with baton-wielding police in the early hours of Tuesday as interior troops and riot police forced protesters and removed barricades from around the government headquarters in the capital Kiev.
"More than 10 people are injured," a lawmaker from nationalist Svoboda (Freedom) party, Yuriy Syrotyuk, told AFP. He said one suffered punctured lungs and several had broken arms or legs.
The authorities said two police officers were injured in a crush.
Ukrainian President Viktor Yanukovych was due to meet EU mediator Ashton in Kiev for talks aimed at solving the crisis sparked by Ukraine's decision to reject a pact with the European Union in favour of a trade alliance with Russia.
He was also due to meet on Tuesday with three former Ukrainian presidents -- Leonid Kravchuk, Leonid Kuchma and Viktor Yushchenko -- in a bid to find a way out of the crisis and was also backing the idea of roundtable talks with the opposition.
The opposition said it would not sit down for talks with the authorities before Yanukovych dismissed the government, punished riot police for crushing a smaller protest last month and released arrested demonstrators.
"A round table does not fit very well in a square prison cell," said opposition leader Arseniy Yatsenyuk.
The party of jailed opposition leader Yulia Tymoshenko said that armed law enforcement officers had raided its headquarters, taking away documents and servers.
Ashton voiced concern Tuesday that any attempts to end the stand-off between Ukrainian security forces and pro-EU demonstrators could be derailed by the raid on opposition party offices.
"These latest events seriously risk to derail the process," she said, calling on the Ukrainian authorities "to exercise utmost restraint and refrain from any further use of force, in order to give space for a negotiated solution out of the current political stalemate."
And US Vice President Joe Biden on Monday conveyed Washington's "deep concern" to Yanukovych.
Biden had called Yanukovych and emphasised the "need to immediately de-escalate the situation and begin dialogue with opposition leaders", a White House statement said.
Assistant Secretary for Europe Victoria Nuland on Monday met Russian leaders in Moscow to voice US concern about the situation in Ukraine.
Nuland "made clear to Russian counterparts that the US supports Ukraine's European choice, a non-violent and just political resolution to the current standoff, and a return to economic health with the support of the International Monetary Fund," the State Department said in a statement.
The website of the Zerkalo Nedeli weekly said that Yanukovych on Monday had held a special meeting of his top security officials and ministers at his out-of-town residence where it was decided to restore order in central Kiev.
The protesters kept up their stand, with around 350 people braving temperatures of around -7 degrees (19 degrees Fahrenheit) and falling snow to spend another night on Kiev's Independence Square.
Hundreds of thousands on Sunday filled Independence Square and dozens of masked protesters tore down a statue of Lenin after putting a rope noose round his neck.
Police opened a criminal probe into "mass riots" over the felling of the monument but said Monday that so far no-one had been arrested over the incident.
The size of Sunday's protest, the third mass rally in successive weekends, increased the pressure on Yanukovych, who further galvanised his opponents by meeting Russian President Vladimir Putin in almost total secrecy on Friday.