Hundreds of police have moved into a large protest camp in the centre of Kiev.
Protesters shouted "Shame!", "We will stand!" and sang the Ukrainian national anthem.
The storming of the camp at Independence Square comes despite a visit by two senior Western diplomats to try to defuse a weeks-long stand-off between the opposition and president Viktor Yanukovych.
The police tried to dismantle barricades surrounding the camp, but then moved back after resistance from protesters. The police have taken up position on the perimeters of the camp.