People killed as riot police and troops attack protesters in Kyiv (Video, online)

The police used grenades and firearms.

The clashes began after police moved in to dismantle a protest camp.

A brutal operation on Hrushevsky Street in Kyiv started at 8 a.m. (10 a.m. Minsk time). The riot police and special forces attacked the protesters' barricades. Gunshots were heard during the attack. The police approached the buses, which were burnt two days ago. Videos showed people trying to escape and policemen catching and beating them.

Four people are reported to have died in clashes. Three protesters, among them activist Sergei Nigoyan, were shot by the police. Another protester died at hospital after he had fallen from the top of the stadium.

Protesters threw firebombs and stones, while the police used tear gas and rubber bullets. At least one of the men who died had bullet wounds.

The violence was triggered by the introduction of new laws last week that criminalise protests.

The deaths are thought to be the first fatalities since demonstrators began camping out in central Kiev in late November, in anger at the government's rejection of a planned treaty with the EU in favour of Moscow.

Wednesday's violence was restricted to a small area around Hrushevskyy Street, close to the main protest encampment at Maidan (or Independence Square).

Prime Minister Mykola Azarov told his cabinet on Wednesday that "terrorists" from Maidan had "seized dozens of people and beat them".

"I am officially stating that these are criminals who must answer for their action," he said.

Meanwhile, the US embassy in Ukraine said it had revoked the visas of "several Ukrainians who were linked to the violence". It did not give names, but said it was "considering further action against those responsible for the current violence."

Hundreds of people have been injured during the three nights of clashes, though peaceful protesters have blamed a little-known far-right group, Right Sector, for carrying out the violence.

Fireworks

Shortly after 06:00 GMT on Wednesday - after a relatively peaceful night - police stormed protesters' barricades on Hrushevskyy Street.

Fresh clashes broke out as police arrested protesters, amid heavy snowfall.

Protesters could be seen on live TV coverage throwing stones and fireworks towards police. At least one police officer threw a firebomb towards a burned bus.

The BBC's Duncan Crawford in Kiev says police have now fallen back and protesters are returning to the square.

Officials confirmed the deaths of two people, found with gunshot wounds. The general prosecutor said their bodies were found in a national library close to the scene of the clashes.

Medics for the activists say at least one person had multiple wounds and claimed he had been killed by a police sniper.

A third activist is also reported to have died on Wednesday from injuries sustained after falling from the top of the Dynamo football stadium.

Many of the protesters have been wearing red helmets, in defiance of the new laws, which ban protective headgear and masks at protests.

The laws also prescribe jail terms for anyone blockading public buildings and outlaw unauthorised tents in public areas.