Vice President Joe Biden called Ukraine's president, Viktor Yanukovich, on to express grave US concern at rising violence in Kiev and to urge him to pull back government forces and exercise maximum restraint.
The vice president further underscored the urgency of immediate dialogue with opposition leaders to address protesters' legitimate grievances and to put forward serious proposals for political reform.
On a day Ukrainian riot police charged protesters occupying a central Kiev square, Biden made clear to Yanukovich that the United States condemns violence by any side, "but that the government bears special responsibility to de-escalate the situation," a White House statement said.
It said the United States is committed to supporting efforts to promote a peaceful resolution to the crisis in a way that "reflects the will and aspirations of the Ukrainian people."
Ukraine's interim President has expressed concerns about signs of separatism as opposition in Russian-speaking regions grows.
Hundreds of Ukrainians and journalists flocked to the presidential palace, as reports emerged that President Yanukovich had left the city.
Vitali Klitschko was met with boos from anti-government protesters, as he attempted to convince them a peace deal is best course of action.