Riot police have begun dismantling protesters' barricades that have been blocking access to government buildings in Kyiv.
The police moves came amid a tense standoff following neary three weeks of protests over President Viktor Yanukovych's decision not to sign a landmark agreement on closer ties with the European Union. Instead, he sought closer ties with Russia.
There were no immediate reports of clashes as riot police removed barricades outside the main government building.
However, some clashes between police and protesters were reported early on December 10, with some protesters reportedly wounded.
The opposition Batkivschyna party said heavily armed riot police stormed its headquarters in the capital, seizing computer servers and other equipment.
The Interior Ministry, after initially denying any police involvement, said the raid was carried out in connection to a criminal investigation.
Vitaliy Klitschko, the leader of the opposition UDAR party, appealed to riot police not to use force. He also warned that Yanukovych would bear "personal responsibility" if the police crackdown turns violent.
"There are no fighters here. These are ordinary people. There are members of parliament here. I ask you -- each of you -- before you get an order [to clamp down on protests], please think about what you do," Klitschko said.
"Do you break the law? Because if you do, you will have to answer for that. There are peaceful people here. None of us has either guns or other objects. This is a peaceful demonstration."
State prosecutor Viktor Pshonka warned protesters to end their blockades and stop "testing the patience of the authorities."
Ukraine's Security Service (SBU) announced earlier that it had opened an investigation into alleged attempts by unnamed politicians to seize power.
Yanukovych said on December 9 he supports roundtable talks involving the opposition to defuse the crisis.
Yanukovych said the "all-national roundtable" proposed by Ukraine's former President Leonid Kravchuk could become "a platform for understanding." A date was not given for when those talks might begin.
WATCH: A statue in downtown Kyiv is torn down on December 8, the heaviest day of protests since the Ukrainian government signaled its decision to back out of talks for an EU Association Agreement more than two weeks ago.
Yanukovych also announced that he plans to meet on December 10 with Kravchuk and two other former presidents, Leonid Kuchma and Viktor Yushchenko, to seek a way out of the crisis.
U.S. Vice President Joe Biden has telephoned Yanukovych to express Washington’s concerns about the political crisis and the growing potential for violence. A statement issued by the White House says Biden told Yanukovych that violence has no place in a democratic society and is incompatible with the strategic relationship between Ukraine and the United States.
Biden also told Yanukovych that the situation on the streets of Kyiv needs to be immediately deescalated and that talks should begin soon with opposition leaders to develop a consensus on how the country can move forward.
The European Union has called on Ukrainian authorities not to respond with violence against protesters.
Lithuania, which currently holds the EU presidency, warned that the use of force would "burn bridges for dialogue."
The EU's foreign policy chief Catherine Ashton plans to be in Kyiv on December 10-11 to try to help defuse the political crisis.
WATCH: A bird's-eye view of the December 8 protests in Kyiv is captured by RFE/RL Ukrainian Service correspondent Andriy Dubchak.
With reporting by UNIAN, Reuters, and AFP