More than 200 people were injured and over 20 were arrested in clashes involving police and opposition demonstrators in the Ukrainian capital that lasted until the wee hours of Monday, according to an initial tally.
A total of 103 demonstrators required medical assistance, 42 of whom were hospitalized, Ukrainian health officials said.
More than 100 police also were injured in the street battles, 61 of whom had to be hospitalized, according to the latest Interior Ministry figures.
The clashes erupted at the end of a massive opposition rally that attracted more than 100,000 people Sunday to Kiev's Independence Square, where more than two months of pro-European Union protests have been staged.
The incidents began when several thousand protesters tried to break through a police cordon set up outside the parliament building, at a distance of roughly 500 meters (1,640 feet) from the plaza.
More than 20 people were arrested for provoking "mass disturbances," including representatives of various opposition political parties, the Interior Ministry said.
Radio Libertad said several of its journalists were taken into custody while filming the latest clashes early Monday pitting demonstrators against anti-riot police.
Police used tear gas, rubber bullets and water cannon against the demonstrators, who set four police vans and two trucks ablaze.
Downtown Kiev was calm late Monday morning, although tensions remained high with hundreds of demonstrators still gathered at Independence Square and behind the police cordon protecting the parliament building.
Demonstrators on Sunday continued to press their demand that Ukrainian President Viktor Yanukovych resign and to denounce new anti-protest legislation passed last week by ruling-party lawmakers that they say violate basic rights.
Former heavyweight boxing champ and current leader of the opposition UDAR (Punch) party Vitali Klitschko tried to intervene to ease tensions but his efforts proved fruitless and he was even sprayed with powder from a fire extinguisher.
The opposition leader, however, met Sunday night with Yanukovych and expressed his alarm over the clashes.
"I told him the situation is on the verge of a civil conflict, that if the problems put forth by the people are not resolved irreversible processes could be set in motion," Klitschko told public television.
After the meeting, Yanukovych issued instructions for a working group to be formed to resolve the political standoff, the Ukrainian presidency's press office said.
On Monday, Klitschko's party said on its Web site that the opposition politician was demanding that the president negotiate directly with protesters and not through intermediaries.
Anti-government protests erupted in Ukraine in November after Yanukovych backed away from plans to ink a free-trade deal with the European Union.
He later signed a $15 billion loan package with Russia and negotiated a deal to enable Ukraine, a former Soviet state, to purchase natural gas from its neighbor at a steep discount. EFE