Vladimir Putin appears all but certain to return to the Kremlin in Sunday's Russian presidential election, but he will find himself in charge of a country far more willing to challenge him.

An unprecedented wave of massive protests showed a substantial portion of the population was fed up with the political entrenchment engineered by Mr Putin since he first became president in 2000, and police are already preparing for the possibility of post-election unrest in Moscow.

The Putin system of so-called "managed democracy" put liberal opposition forces under consistent pressure, allowing them only rare permission to hold small rallies and bringing squads of police to break up any unauthorised gathering.

The Kremlin gained control of all major television channels and their news reports turned into uncritical recitations of Mr Putin's programs, often augmented with admiring footage of him riding horseback, scuba-diving or petting wild animals.

But the protests, sparked by allegations of widespread fraud in December's parliamentary elections, forced notable changes.

Authorities gave permission, however grudgingly, for opposition rallies that attracted vast crowds, upward of 50,000 in Moscow. State television gave them substantial and mostly neutral coverage.

Whether that tolerance will last after the election is unclear. According to the most recent survey by the independent Levada Centre polling agency, Mr Putin is on track to win the election with around two thirds of the vote against four challengers - enough to bolster his irritable denunciations of the protesters as a small, coddled minority.

Mr Putin has repeatedly alleged that the protesters are stooges of the United States and Western European countries that want to undermine Russia and he has insulted them, saying for instance that their white ribbon emblems looked like condoms.

In the past week, the rhetoric became even harsher as Mr Putin publicly suggested the opposition was willing to kill one of its own figures in order to stoke outrage against him. That claim came on the heels of state television reports that a plot by Chechen rebels to kill Mr Putin right after the election had been foiled.

Some of Mr Putin's election rivals dismissed the report as a campaign trick to boost support for him.

Protests after the election appear certain.

"People in Russia are not going to recognise Putin's victory in the first round," Alexei Navalny, one of the loosely knit opposition's most charismatic figures, declared flatly this week.

Another prominent protest figure, Ilya Ponomarev, a parliament member from the opposition A Just Russia party, said the protesters' mood has become more truculent as authorities consistently brushed off their initial demands for nullifying the results of the December parliament election.

"It has evolved from 'we demand a rerun' to 'go to hell'," he said.

The Interior Ministry is calling in 6,000 police reinforcements to the capital from other regions, the state news agency ITAR-Tass reported yesterday.

Whether tomorrow's vote is seen as honest is likely to be key; a count without reports of wide violations could deprive protesters of a galvanising issue.

As the first protests roiled the country, Putin announced an expensive program to place two web cameras in each of the country's 90,000 polling stations, one showing a general view and one focusing on the ballot box. However, their effectiveness is in doubt.

"Cameras cannot capture all the details of the voting process, in particular during counting," the election observation mission of the Organisation for Security and Co-operation in Europe noted in a report on election preparations.

Along with the OSCE mission, tens of thousands of Russians have volunteered to be election observers, receiving training for activist groups on how to recognise vote-rigging and record and report violations.

Mr Putin has promised to appoint Dmitry Medvedev prime minister if he wins the presidency in order to pursue his reform ideas, but many regard Mr Medvedev as lacking the hard-edge political skills to be an effective reformer.

None of the other candidates have been able to marshal a serious challenge to Mr Putin. The Communist Party candidate, Gennady Zyuganov, gets support of about 15%, according to the Levada centre survey, which claimed accuracy within 3.4 percentage points.

The others - nationalist firebrand Vladimir Zhirinovsky, Sergei Mironov of A Just Russia and billionaire Mikhail Prokhorov - were in single digits.