Ukrainian President Viktor Yanukovich backed a call for talks with the opposition on Monday to end weeks of protests in Kiev, but tension was high with pro-Europe demonstrators barricading their protest camp in preparation for police intervention.

As riot police took up new positions in the capital, heavyweight boxing champion-turned-opposition politician Vitali Klitschko called on the protesters to stand their ground, and warned Yanukovich that he would have blood on his hands if security forces tried to end the stand off violently.

With pressure growing on a shaky economy, the presidential website said Yanukovich supported a proposal for round-table talks involving the authorities and the opposition as a possible "platform for mutual understanding", the website said.

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No date was given for when the reconciliation talks could be held. Nor was it clear what the united opposition's reaction to Yanukovich's proposal would be.

But it was the first real sign by Yanukovich - whose switch in trade policy away from the European Union towards Russia on November 21 provoked the unrest - that he might be ready to listen to opposition demands for the resignation of his government and early elections.

Despite his words, tension rose sharply on the streets after riot police units moved to take up their positions at potential flashpoints. Demonstrators, responding to calls from opposition leaders, threw up new blocks in streets blanketed by snow after a heavy fall overnight to seal off their main protest camp on Kiev's Independence Square.

"The opposition must stay here and do everything to stop the police from breaking up a peaceful demonstration," Klitschko told Reuters.

"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 Klitschko, who is increasingly seen as a national leader-in-waiting in recent weeks.

"We are expecting the break-up by police of peaceful demonstrators. If blood is spilled during this dispersing (of protesters), this blood will be on the hands of the person who ordered it ... Yanukovich," Klitschko said.

The protesters have been inflamed by a police crackdown on November 30 and European Commissioner Jose Manuel Barroso, who spoke to Yanukovich by phone on Sunday, led Western calls on Monday for authorities not to react violently.

"Those young people in the streets of Ukraine in freezing temperatures are writing the new narrative for Europe," he said in Milan. "I've asked him (Yanukovich) to show restraint in the face of these recent developments, not to use force against people who are demonstrating peacefully, to respect fully their freedom."

EU foreign policy chief Catherine Ashton expects to meet Yanukovich and opposition leaders when she visits Kiev on Tuesday and Wednesday.

— The Associated Press and Reuters contributed to this report