Fires raged in Kiev's main protest camp on Independence Square as riot police tried to force demonstrators out following the bloodiest clashes in three months of protests.
The iconic square turned into a war zone as riot police moved in slowly from several directions to push back opposition lines, hurling stun grenades and using water cannon to clear protesters.
Demonstrators responded by throwing Molotov cocktails and rocks at security forces and set fire to one of the police water cannon trucks.
Television footage from the scene showed protesters capturing several riot police in fierce clashes before dragging them away through the crowd as demonstrators aimed punches at them.
Protesters burned tyres and any wood they could lay their hands on, sending a thick smokescreen into the night sky to hide them from riot police.
Around a quarter of the tents were on fire in the sprawling encampment, where protesters have been camped out demanding President Viktor Yanukovych leave power since he ditched a closer ties with the EU in favour of Russia.
Police had warned women and children through loudspeakers to leave the area as the assault began, saying that they were launching "an anti-terrorist" operation. But thousands of people remained on the square.
Exhorting the crowd from a stage in the square where protest leaders continued to speak as the assault was continuing, opposition leader Vitali Klitschko said that protesters "were not going anywhere".
"This a small island of freedom," the former heavyweight boxer said.
Klitschko added that Yanukovych had called him offering negotiations but had been told to first withdraw the riot police.
A spokesman for Klitschko later said that the opposition chief had headed to Yanukovych's residence just before midnight for talks. But an hour later opposition representatives at the protest camp said that they were still waiting for the meeting to happen.
Police said that seven police officers had been killed in yesterday's clashes, all of them dying from gunshot wounds.
Authorities and demonstrators said five civilians were also killed in the clashes, while two more were found dead with no exterior signs of violence.
Kiev was in essential lockdown as authorities halted the city's metro system and said limited road traffic coming into the capital from midnight (2200 GMT).
