Masked protesters hurled Molotov cocktails and rocks at thick lines of armed anti-riot troops in Kiev's central Independence Square, the epicenter of the ex-Soviet country's three-month-old political crisis.

The demonstrators pushed police forces back some 200 meters to retake control of the entire square, which anti-government protesters have occupied since November.

Police used rubber bullets to try to repel the assault and claimed that a sniper had wounded 20 officers by firing live ammunition from the window of a building overlooking the smoke-filled square.

The main government building nearby was evacuated following the violence.

The clashes shattered a truce that Ukrainian President Viktor Yanukovych had called with the opposition just hours earlier, after a spurt of violence killed more than two dozen people in less than two days.

Yanukovych was holding crisis talks with the foreign ministers of France, Germany and Poland, ahead of an emergency meeting in Brussels where the EU is expected to impose sanctions against the Ukrainian government for the violence.

The EU envoy meeting was reported to have been cancelled, but a Ukrainian presidential spokesman told AFP that the encounter was being held after all.

Yanukovych has appeared to struggle to formulate a clear policy over the past few days, which have seen Ukraine's deadliest violence since independence.

NJF/NJF