Police fired volleys of rubber bullets to try and repel the attack while protesters pelted them with Molotov cocktails and rocks and set a bus on fire.

The protesters managed to push back the police forces about 200 metres, regaining control of barricades at the entrance to the square that they had occupied since the start of Ukraine's three-month-old political crisis.

Frantic medics treated people at the scene.

An AFP journalist saw at least eight wounded people being carried through the crowd on stretchers, two in a serious condition.

On the stage in the center of the protest camp-- which has turned from a bustling tent city into a scorched war zone of debris and fires over the past few days -- speakers beseeched some of the thousands of people elsewhere on the square to reinforce barricade over fears of a police response.

The violence erupted just hours after Ukraine's embattled President Viktor Yanukovych and main opposition leaders called a truce after clashes between anti-government protesters and security forces killed 28 people, the worst violence to wrack the ex-Soviet country since its independence in 1991.

NJF/NJF