International monitors said Russia's presidential election was clearly skewed to favour Vladimir Putin, a verdict that could spur protesters planning to take to the streets to challenge his right to rule.

Putin, who secured almost 64 percent of votes on Sunday, portrayed his emphatic victory for a third term as president as a strong mandate to deal with the biggest anti-Kremlin protests since he rose to power in 2000.

But hours before protests were planned to start in central Moscow, vote monitors from the Organization for Security and Co-Operation in Europe echoed his opponents' complaints that the election was slanted against them.

The point of elections is that the outcome should be uncertain. This was not the case in Russia, Tonino Picula, one of the vote monitors, said on Monday. According to our assessment, these elections were unfair.

French Foreign Minister Alain Juppe said the election had not been exemplary to say the least.

Monday's opposition rally was to take place at Pushkin Square, often the site of Soviet-era dissident protests swiftly smothered by KGB officers. Some opposition leaders received official warnings not to try to march towards the Kremlin for fear of clashes.

Rallies in support of Putin were scheduled close to the Kremlin's redbrick walls.

Tiny Cox, one of the most senior electoral monitors, said there had been some improvements from a parliamentary poll which observers said was marred by irregularities on December 4

We did not see the violations we saw in December. We saw far less cases of ballot-box stuffing, he said.

But the OSCE monitors said Putin still had an advantage over his rivals in the media and that state resources were used to help him extend his domination of Russia for six more years.

Expressing concerns which a European Union spokeswoman said were shared by the 27-country bloc, the monitors called for all allegations of irregularities to be thoroughly investigated.

Although the observers' findings have no legal bearing, they undermine Russian election officials' statements that there were no serious violations.

They would also support some in their view that elections ultimately have little real significance in Russia; that power is something tightly controlled and divided up by a largely stable ruling clique, as demonstrated by the 'tandem' power deal struck by Putin and current president Dmitry Medvedev in 2008.

It's not the people who choose, it's the authorities who choose themselves. It's all just a game put on for the people, an advertisement for Putin, said Agil Alekberov, who works in a Moscow home furnishings store.

Putin's opponents, fearing he will smother political and economic reforms, have refused to recognise the result, which could allow the former KGB spy to rule Russia for as long as Soviet leader Leonid Brezhnev, accused of presiding over the years of stagnation.

Putin has already served as president or premier for 12 consecutive years and made way for his ally Medvedev in 2008 only because of constitutional limits.

He (Putin) is forcing things to breaking point. He is declaring war on us, said journalist Sergei Parkhomenko, one of the protest organisers.

OLIVE BRANCH

In a conciliatory move, Putin invited his defeated presidential rivals to talks, although Communist Party candidate Gennady Zyuganov did not attend. Putin also sought to show he is aware of voters' concerns about corruption by discussing efforts to crack down on graft with an aide.

The Kremlin also took steps that appeared intended to try to take the sting out of the protests which began over the December 4 poll won by Putin's United Russia party.

Medvedev, who will stay in office until early May, told the prosecutor general to study the legality of 32 criminal cases including the jailing of former oil tycoon Mikhail Khodorkovsky.

Khodorkovsky, who headed what was Russia's biggest oil company, Yukos, and was once the country's richest man, was arrested in 2003 and jailed on tax evasion and fraud charges after showing political ambitions and falling out with Putin.

The Kremlin said Medvedev had also told the justice minister to explain why Russia had refused to register a liberal opposition group, PARNAS, which has been barred from elections.

The order followed a meeting last month at which opposition leaders handed Medvedev a list of people they regard as political prisoners and called for political reforms.

Medvedev's initiatives have only one goal: To at least somehow lower the scale of dismay and protest that continues to surge in society, Zyuganov said.

The move could be a stalling tactic intended to appease the organisers of the biggest protests of Putin's rule, or it could be a parting gesture by a man intent of making his mark as the more liberal of the ruling tandem with Putin.

PUTIN DIVIDES OPINION

Almost complete election results on Monday showed Putin, 59, had won almost 64 percent of votes.

Zyuganov was second on just over 17 percent and liberal billionaire Mikhail Prokhorov had almost 8 percent. Nationalist Vladimir Zhirinovsky secured just over 6 percent and former parliamentary speaker Sergei Mironov had less than 4 percent.

There were practically no serious violations, Central Election Commission chief Vladimir Churov told reporters, dismissing the allegations of irregularities across Russia by the opposition and volunteer vote monitors.

Golos, an independent monitoring group, said it had registered at least 3,100 reports of violations nationwide.

Many voters, especially in the provinces, see Putin as a safe pair of hands and credit him with restoring order after the chaotic 1990s under President Boris Yeltsin and overseeing an economic boom.

But others have lost all faith in elections and see Putin as an impediment to Russia having a fair, decent society.

We've had enough lies. The whole country has had enough lies, said Rosa Trukachova, a 60-year old pensioner.

(additional reporting by Jennifer Rankin and Katya Golubkova; writing by Timothy Heritage; editing by Elizabeth Piper)