Riot police moved in on protest camps in central Kiev in the pre-dawn hours of Wednesday, dismantling barricades, tearing down tents and detaining several demonstrators, who shouted "Shame!" as the bells of the capital's major Orthodox cathedral tolled through the night.
Police tore down barricades surrounding the tent camp on Maidan Nezalezhnosti, or Independence Square, but pulled back as thousands of protesters refused to retreat.
The Interior Ministry said several protesters have been detained for resisting the police. The opposition put the number of detainees at 11 people or more, Lenta.ru reported.
Officials said police was acting on court orders banning mass rallies in the center of the city, in an escalation of the standoff that began with the Ukrainian government's rejection of a planned association deal with the European Union and has grown into a massive protest against the rule of President Viktor Yanukovych.
The ranks of protesters swelled through the night, as cab drivers drove supporters to the square free of charge and more demonstrators joined the crowd through gaps in the police cordon around the perimeter, RIA Novosti reported.
Smoke clouds gathered above sections of the barricades, as one of the protesters' tents caught fire and pyrotechnics went off in the air. Many protesters wore construction workers' helmets to protect their heads against possible blows, following last week's clashes between police, special troops and demonstrators that left several dozen people injured.
From a makeshift stage in the middle of the square, speakers urged protesters not to fight the troops, stressing that theirs was a peaceful protest, and appealed to the police "not to follow criminal orders," Interfax reported.
Ukrainian singer Ruslana, winner of the World Music Award and the Eurovision Song Contest in 2004, was joined by scores of demonstrators as she sang the national anthem.
The police raid came hours after EU foreign policy chief Catherine Ashton met with Yanukovych in an attempt to defuse the crisis.
In a statement on Facebook, Ashton told protesters: "I was among you on Maidan in the evening and was impressed by determination of Ukrainians demonstrating for European perspective of the country."
"Some hours later I observe with sadness that police uses force to remove peaceful people," she said. "The authorities didn't need to act under the coverage of night to engage with the society by using police."
U.S. Secretary of State John Kerry also condemned the Ukrainian authorities' response.
"The United States expresses its disgust with the decision of Ukrainian authorities to meet the peaceful protest in Kiev's Maidan Square with riot police, bulldozers, and batons, rather than with respect for democratic rights and human dignity," he said in a statement published on the U.S. State Department website.
"This response is neither acceptable nor does it befit a democracy," he said.