Russia's presidential elections were "clearly skewed" in favour of Vladimir Putin and "lacked fairness", international election monitors have reported as Putin celebrated returning to the Kremlin for a third term.
In a statement issued on Monday, the Organisation for Security and Co-operation in Europe, said that voting had been "assessed positively overall and had produced a clear winner with an absolute majority".
But it said: "Voter's choice was limited, electoral competition lacked fairness and an impartial referee was missing."
Tonino Picula, who headed the OSCE observer mission, said: “There were serious problems from the very start of this election. The point of elections is that the outcome should be uncertain. This was not the case in Russia. There was no real competition and abuse of government resources ensured that the ultimate winner of the election was never in doubt.”
Putin, who has dominated Russian politics since the beginning of the 21st century, won almost 64 per cent of votes, Russia's Central Election Commission said.
But the scale of Putin's victory was questioned by some of his rivals, and opposition activists, who called for protests later on Monday over allegations of vote-rigging.
Putin's Communist rival Gennady Zyuganov , who finished in second place with about 17 per cent of votes, called the vote "crooked, absolutely unfair and unworthy," while a leading opposition activist, Vladimir Ryzhkov, said "these elections cannot be considered legitimate in any way".
Echoing concerns among his opponents, Catherine Ashton, the European Union's foreign affairs chief called on Russia to address shortcomings raised by the OSCE.
But German Chancellor Angela Merkel would call Putin to wish him success in his presidency, while Chinese President Hu Jintao congratulated Putin on his victory.
Russia witnessed popular protests on a scale unseen since the 1990s amid widespread allegations of fraud following last year's parliamentary elections, and some are now hoping for a repeat of those scenes.
Addressing tens of thousands of supporters in Moscow late on Sunday, a tearful Putin said the Russian people had clearly rejected the attempts of unidentified enemies to "destroy Russia's statehood and usurp power", and said the contest had been "open and fair".
"The Russian people have shown today that such scenarios will not succeed in our land," said Putin, flanked by outgoing President Dmitry Medvedev. "They shall not pass!"
"I promised you we would win. We have won. Glory to Russia. We won in an open and fair struggle."
'We do not accept these results'
Garry Kasparov, the former chess world champion who is now an outspoken critic of the Russian government, told Al Jazeera's Barnaby Phillips in Moscow's Red Square: "We do not accept these results. It's back to the streets"
Putin served two terms as president between 2000 and 2008, before stepping aside to become prime minister under Dmitry Medvedev because of Russia's two consecutive-term limit.
Al Jazeera's Christopher True, reporting from Moscow, said: "There has been a mixed reaction to Putin's victory on the streets of Moscow.
"Many Muscovites said that even if Putin won, they did not believe he could have genuinely taken almost two-thirds of the vote."
But some commentators have defended the election.
Speaking to Al Jazeera, Vyacheslav Nikonov, a Russian political scientist, said: "The elections were fair, observers from the opposition were looking at every ballot and voter and checking the process very closely.
"Of course, we know that protests will take place here anyway, however transparent the voting process is."
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Many Russians credit Putin with restoring the country's prestige and influence on the international stage after the chaos and financial collapse of the country in the 1990s following the end of the Soviet Union.
But critics accuse Putin of authoritarian tendencies and say he has failed to root out pervasive corruption.
Sergei Strokan, a political analyst in Moscow, told Al Jazeera that “while the vast majority of Russians are satisfied with a candidate like Vladimir Putin, still there is a minority which considers his vision of the world to be obsolete.
"This is really a challenge for Vladamir Putin because he will have to find the proper message for these people and it seems so far that he’s lacking this message as we are only hours before a mass opposition rally ... in downtown Moscow.”
Putin's share of the vote was down from the nearly 72 per cent he won in 2004; a result repeated by Medvedev, Putin's hand-picked successor in 2008.
An interior ministry spokesperson said there had been no major violations. Ria Novosti news agency quoted a source in that Dagestan election commission as saying the results at a polling station where apparent ballot stuffing was observed through the live web cams would be cancelled.