KIEV/MOSCOW  - At least seven people were killed and scores injured on Tuesday as anti-government protestors battled riot police in Kiev in the first outbreak of violence in weeks. Police said seven people have died in clashes that prompted the city to shut down the subway system and issued a grave warning to protesters, with riot police troops massing near the Independence Square protest hub.

EU foreign policy chief Catherine Ashton on Tuesday denounced the “grave new escalation” in Kiev, where at least five people were killed and scores hurt as protestors battled police.

“I am deeply worried about the grave new escalation in Kiev and the reported victims,” Ashton said in a statement, saying she condemned “all use of violence, including against public or party buildings.”

Medics working at field hospitals run by the opposition earlier said that three protesters died of gunshot wounds and that around 150 others were injured, of which some 30 were in a serious condition.

Yanukovych’s ruling Regions Party said that an employee at its headquarters was also found dead after protesters briefly seized the building.

Police said that 47 servicemen had been injured, including five with bullet wounds, as parts of Kiev resembled a war zone with demonstrators and security forces fighting pitched battles in locations close to Ukraine’s parliament building.

Security forces issued an ultimatum warning that they would use “grave actions” to restore calm if unrest persisted until 18.00 (1600 GMT). Kiev also shut down vast subway network for the first time in the three month-long crisis. “If unrest continues we will be forced to take grave actions,” Ukraine’s interior ministry and state security agency warned in a joint statement.  Riot police had succeeded in forcing protesters back into their camp on Kiev’s iconic Independence Square after heavy reinforcements arrived.

Tuesday marked the first violent clashes since mid-January in the Ukrainian capital, which has been wracked by anti-government demonstrations since Yanukovych in November rejected an EU pact in favour of closer ties with historical master Russia. Protesters briefly seized Yanokuvych’s party headquarters after several hundred attacked it with Molotov cocktails and smashed their way inside but later withdrew as smoke continued to billow from part of the building, an AFP reporter at the scene said.

Fighting flared after some 20,000 mainly peaceful protesters marched from their sprawling tent encampment towards parliament to demand legislators strip the president of a raft of powers.

Police fired rubber bullets and hurled smoke bombs and stun grenades at protesters who threw paving stones and set two trucks on fire trying to break through to the heavily-fortified parliament.

Demonstrators were calling on the Rada parliament - where Yanukovych’s party has a majority - to vote on returning the country to its 2004 constitution, under which key powers would shift from the president to parliament.

“People were tired of waiting for the constitution to be changed- they needed action,” said demonstrator Volodymir, from Kiev, refusing to give his second name. Another protestor Anatoli, also from Kiev, said that the latest Tuesday’s protests could outstrip January’s brutal clashes when several protestors were killed.

“I think the actions will be on a bigger scale than they were on Grushevsky street (where January’s fatal clashes happened),” he said. “We need to surround the parliament until there is a complete change of government.”

Opposition leaders called on Yanukovych to give into their demands if he wanted to defuse the violence.

Meanwhile, a top Russian lawmaker, who oversees foreign affairs, said that Ukraine is on the brink of a civil war that has been inflamed by the West.

Alexei Pushkov, the head of the lower house's foreign affairs committee, condemned the deadly violence that erupted in Kiev -- at least seven people have been killed on Tuesday -- as an attempt to "seize power through chaos and lawlessness" in comments to the Interfax news agency.

"I consider that a significant amount of responsibility for this falls on the West and Western politicians, who are constantly putting pressure on the Ukrainian authorities," Pushkov said.

He said Western powers had prevented the authorities from cracking down on "these ultra-radical organisations that are now shooting at police and special forces and are leading the situation to civil war".

"Talking about the need to protect the democratic will of the Ukrainian people and the campaign of pressure on the Ukrainian authorities could well lead to a civil war starting there," he added.

"In fact, it is already present, in embryonic form."

The Russian foreign ministry earlier Tuesday had blamed the policies of Western countries for the clashes.

"What is happening is a direct consequence of the policy of connivance among those Western politicians and European agencies that have been shutting their eyes to the aggressive actions of Ukraine's radical forces," the ministry said in a statement.