US Vice President Joe Biden on Monday conveyed Washington's "deep concern" to Ukrainian leader Viktor Yanukovych as tensions escalated in the country's political crisis.

Biden had called Yanukovych and emphasized the "need to immediately de-escalate the situation and begin dialogue with opposition leaders," the White House said in a statement.

Biden's call came after Ukrainian security forces moved in on pro-EU demonstrators to end a week-long blockade of the government headquarters.

Protestors have taken to the streets after Yanukovych refused to sign a European Union pact under pressure from Moscow.

The White House statement said Biden had warned against violence saying it "has no place in a democratic society and is incompatible with our strategic relationship."

Assistant Secretary for Europe Victoria Nuland meanwhile met Monday with Russian leaders in Moscow to voice US concern about the situation in Ukraine, where she last week attended a European security body meeting.

Nuland had "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.

"We continue to believe that it's long past time for the leadership to not only listen to the voices of its people, but we continue to encourage them to restore a path to European integration and economic help," State Department spokeswoman Jen Psaki told reporters.

She refused to be drawn on whether the US agreed with some protestors demands that Yanukovych should step down, saying that was "a decision for the people of Ukraine to make."

But she stressed there were some ways in the future that the United States might be able to help Kiev economically, including draft legislation which would make certain Ukrainian products eligible for duty-free entry into the United States.

[Image via Agence France-Presse]