Ukrainian President Viktor Yanukovych has warned bloody clashes between protesters and police threaten all of Ukraine as new fighting rocked the capital Kiev.
The clashes, the worst in Kiev in recent times, marked a spiralling of tensions after two months of demonstrations against Yanukovych's refusal to sign a pact for closer integration with the EU.
Amid growing fears the police could act to violently disperse the protest, Ukraine's Prosecutor General Viktor Pshonka warned protesters to halt "mass rioting", describing it as a crime against the state.
In a second day of clashes after 200 were injured in Sunday's fighting, thousands of Ukrainians braved temperatures of minus 10C to take part in the standoff with police.
The protesters in central Kiev lobbed stones dug up from the cobbled road, flung Molotov cocktails and threw fireworks over a 20-metre no-man's land at police lines.
Police responded by throwing stun grenades and occasionally using rubber bullets and tear gas.
"I am convinced that such phenomena are a threat not only to the public in Kiev but all of Ukraine," Yanukovych said.
"I urge dialogue, compromise and calm in our native land.
"I ask you not to follow those who urge violence, who are seeking to provoke a split between the state and society."
But even after his comments, some 10,000 protesters remained around the centre of the clashes, with the most radical using lasers to blind police firing stun grenades.
"Who, if not us, and when, if not now," read a banner carried by one group of protesters.
The burned-out wrecks of half a dozen police vehicles torched and destroyed the day earlier were used by the protesters as a barricade.
According to the Kiev health authorities, more than 100 protesters were wounded in Sunday's clashes.
The interior ministry said more than 100 members of the security forces had been wounded, adding that 30 people had been arrested for mass rioting.
US-funded Ukrainian radio station Radio Svoboda said two of its journalists had been arrested on Monday morning while filming at the scene.
Opposition leaders, including former boxing champion Vitali Klitschko and Arseniy Yatsenyuk, appeared unable to have any influence on the hard core of radical protesters and stopped short of supporting their actions.
But Ukraine's jailed former prime minister and opposition leader Yulia Tymoshenko came out in support of those clashing with police, saying she would be with them if she could.
"Protect Ukraine and do not fear anything. Ukraine has no defence other than you. You are heroes," she said in a statement.
The White House urged an end to the violence, with US National Security Council spokeswoman Caitlin Hayden warning that Washington was still considering sanctions against Ukrainian officials.
EU foreign ministers meeting in Brussels on Monday said the government was at fault for adopting repressive laws which allow jail terms of up to five years for those who blockade public buildings and the arrest of protesters wearing masks or helmets. Other provisions ban the dissemination of "slander" on the internet.