Vladimir Putin said his enemies were planning dirty tricks including ballot stuffing and even murder to tarnish Russia's presidential election that the former KGB spy is almost certain to win.

Prime Minister Putin's aides hope a big win in Sunday's vote will take the sting out of an urban protest movement that casts him as an authoritarian leader who rules through a corrupt and tightly controlled political system.

Putin was initially taken aback at the protests, the biggest of his 12-year rule, but he swiftly mounted an aggressive election campaign for the presidency, mobilising thousands of supporters.

Speaking to his campaign staff in Moscow, Putin said his opponents would seek to declare the elections invalid and suggested that unnamed enemies abroad could try to murder opposition figures to stoke unrest.

Certain mechanisms will be used to show that the election was falsified, Putin told his supporters.

Using street slang, he said his opponents living abroad were ready to order a sacrificial murder of a prominent person to ignite protests.

Sorry for the phrase, but they will whack someone and then blame the authorities for it. These sort of people are ready to do anything. I am not exaggerating, Putin said.

Putin, who this week brushed off a reported plot to kill him, did not say what evidence he had, though he was clearly trying to implicate tycoons who fled Russia during his 2000-08 presidency, many of them to Britain or Israel.

Opinion polls show Putin, described as Russia's alpha-dog leader by U.S. diplomats in confidential reports to Washington, will win the election giving him a six-year term in the Kremlin. But the polls also show an increasing dissatisfaction with his rule.

OPPOSITION PROTESTS

Since the protests, which were sparked by a December parliamentary election that the opposition said was rigged, Putin has mixed promises of political reform with Cold War invective against the United States and sometimes crude jokes.

He has faced a daily onslaught of satire on the Russian language internet, with hundreds of anti-Putin cartoon, videos and jokes which vilify him as an out-of-date authoritarian ruler.

The campaign was stormy but I hope there will be no more dirt. I really hope so. It (the campaign) is coming to a close, thank God, said the 59-year old leader.

But the protest leaders, a fragmented group of politicians, activists, journalists and bloggers, say Putin has not met any of their demands such as a re-run of the December 4 parliamentary election and the sacking of the election commission chief.

Opposition leaders are preparing rallies for the day after the election and say the vote cannot be legitimate because Putin has not allowed a fair playing field for opposition candidates.

Russian police Wednesday prevented a group linked to blogger Alexei Navalny, one of the most influential opposition figures, from distributing tents for activists in central Moscow to be used for longer term protests.

The protesters have put forward clear and concrete demands. None of these demands were met, Navalny told Dozhd television Tuesday. One day people should take to the streets and stay there until their demands are met. This what the tents are for.

(Reporting by Gleb Bryanski; Editing by Rosalind Russell)