Ukrainian police began dismantling protests in front of government buildings in Kiev, BBC News reported on Monday. An opposition party also said that the police raided their headquarters, giving them until Tuesday to vacate the premises. 

Opposition leaders, however, urged supporters to defend Independence Square, the main protest site, in the ongoing weeks of protests.

"The standoff follows weeks of unrest after a U-turn on a free trade deal with the EU," BBC also reported.

"We call on people to stand their ground, and peacefully, without using force or aggression, to defend their right to live in a free country," said heavyweight boxing champion Vitaly Klitschko, a participant in the protests.

"We are expecting the break-up by police of peaceful demonstrators. If blood is spilled during this dispersing, this blood will be on the hands of the person who ordered it: ...[President Viktor] Yanukovych," he added.

Sunday's demonstration was seen as the largest in three weeks, akin to the 2004 Orange Revolution. On Sunday evening, a group of protesters smashed the city's statue of the Vladimir Lenin, "and brought its dismembered parts as trophies to independence Square," according to news reports.

"The demonstrators have condemned Mr Yanukovych for refusing to sign an association agreement with the EU last month. He said he shelved it because it would put trade with Russia at risk," according the BBC also reported.