Ukraine's President Viktor Yanukovych has blamed opposition leaders for the latest upsurge of violence in Kiev, which has left at least 18 people dead.
After failed overnight talks with the opposition, Mr Yanukovych urged its leaders to 'distance themselves from radical forces', saying it was 'not too late to stop the conflict'.
Riot police are continuing to storm the main anti-government protest camp.
Activists blamed the authorities for the worst violence in months of unrest.
Explosions are taking place, fireworks are being thrown and large fires can been seen on Independence Square - known as the Maidan.
The latest assault began shortly after 04:00 local time, when the police tried to move on the protesters' tents. Several were set ablaze.
'Island of freedom'
Security forces had given protesters a deadline of 18:00 local time on Tuesday (16:00 GMT) to leave the square, the scene of a mostly peaceful protest camp since November.
When the deadline expired, riot police advanced with an armoured vehicle, dismantling barricades and firing stun grenades and water cannon.
Protesters have been resisting, throwing missiles from behind huge piles of burning tyres.
In speeches from the main stage through the night, protest leaders urged people already on the Maidan to stand firm, and called on Ukrainians elsewhere to come to the square.
'This is an island of freed.