* Worst street violence since late January
* Opposition want president to cede control of government
* Fresh clashes take place after Russia pledges more aid (Adds analyst comment, Russian central bank)
By Pavel Polityuk and Richard Balmforth
KIEV, Feb 18 (Reuters) - Anti-government protesters clashed violently with police in central Kiev on Tuesday, a day after Moscow moved to cement its influence over Ukraine with $2 billion in cash to shore up the former Soviet state's heavily indebted economy.
A parliamentary deputy said on Facebook that three demonstrators had been killed, and Ukrainian television said five protesters had been hurt in the clashes. Neither report could immediately be confirmed.
Ukraine's defence ministry ordered demonstrators to stop occupying one of its buildings.
The $2 billion injection, a resumption of a $15 billion aid package, was seen as signal that Russia believed President Viktor Yanukovich had a plan to bring street demonstrations under control and had scrapped any idea of bringing opposition leaders into government.
But as protesters and police battled on the streets, Moscow blamed the escalation as a "direct result of connivance by Western politicians and European structures that have shut their eyes ... to the aggressive actions of radical forces".
Russia had seemingly won a struggle for influence over Ukraine with the West with its fiscal package that helped persuade Yanukovich to snub a trade deal with the European Union in November. But protesters who have claimed the centre of the capital, Kiev, as their own are not going quietly.
"I think Russia received some kind of assurances from the Kiev leadership that were satisfactory, because only a day before there was nothing like it," said Gleb Pavlovsky, former Kremlin adviser and political analyst in Moscow.
"I think Yanukovich showed he would stick firmly by his position in talks, he would not make excessive concessions, he would fight the radicals who are getting stronger in the opposition ... and that the (new) prime minister would not be a member of the opposition."
But rather than boosting Yanukovich, Moscow's move may have helped trigger a more violent turn in the protests, especially from those demonstrators who have a strong anti-Kremlin agenda.
Several thousand protesters torched vehicles and hurled stones in the worst violence to rock the capital Kiev in more than three weeks.
Police replied by firing rubber bullets and stun and smoke grenades from trucks and from the tops of buildings, forcing the protesters back by about 100 metres.
"The authorities do not want to compromise on any issue ... We understand that yet another odious candidate will be put forward (for prime minister), one who will be unable to restore the economy or end the political crisis," said Vyacheslav Kyrylenko, an opposition deputy.
Right Sector, a militant far-right group, added to tension by calling on people holding weapons to go to Independence Square, centre of the revolt, to protect it from a possible move by security forces to break it up.
Inside parliament, where opposition leaders brought proceedings to a halt by blocking the speaker's tribune, opposition leader Vitaly Klitschko urged Yanukovich to take riot police off the streets to avert further "conflict in society".
"It will be the decision of a real man," the boxer-turned-politician told reporters inside parliament.
The protesters had marched to the parliament building to press the opposition leaders' calls for Yanukovich to relinquish what they call his "dictatorial" powers and particularly his control of the economy and the security forces.
But when they were blocked by a line of trucks about 100 metres from the building, they hurled stones at police, a Reuters witness said, and set three trucks ablaze with petrol bombs.
As the clashes extended into early afternoon, protesters ransacked a nearby office of Yanukovich's Party of the Regions.
Yanukovich has been battling the opposition-led street protests since he walked away from a trade pact with the European Union in November and opted instead for forging closer economic ties with Russia, Ukraine's Soviet-era master.
The protests have since broadened into a revolt against perceived sleaze and corruption in the Yanukovich leadership.
"WE'RE NOT FOR SALE"
In what has become a geo-political tussle redolent of the Cold War, the United States and its Western allies are urging Yanukovich to turn back to Europe and the prospect of an IMF-supported recovery, while Russia accuses them of meddling.
A senior EU official in Brussels said aid from the European Union and/or International Monetary Fund was still available - tied to reforms.
"It must be done in the context of a Ukrainian government really eager to reform and to do the necessary reform for its economy, in the energy sector in many other sectors, in the modernisation of industry etc," the official, who asked not to be named, said.
News of the fresh credit from Russia failed to cheer the currency market, where the troubled Ukrainian hryvnia fell by up to 1.6 percent against the dollar on Tuesday, Reuters trading system showed.
It also failed to impress the protesters.
"We don't need this money from Russia because it is not meant to help but to buy us. But we are not for sale. Can't they see that this is simply a dirty bribe?," said Valentin Sypko. (additional reporting by Elizabeth Piper in Moscow, writing by Richard Balmforth, editing by Jeremy Gaunt)