Vladimir Putin is set to return to the Kremlin for a third term after claiming victory in Sunday's Russian presidential elections.
Putin, who has dominated Russian politics since the beginning of the 21st century, won about 65 per cent of votes, according to preliminary results from more than 90 per cent of polling stations, Russia's Central Election Commission said.
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".
"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."
But the scale of Putin's victory was questioned by some of his rivals, and opposition activists, who called for protests 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".
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.
'It's back to the streets'
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"
"These are not going to be honest elections, but we must not relent,'' Mikhail Gorbachev, the last leader of the Soviet Union who has grown increasingly critical of Putin, said earlier as he cast his ballot.
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.
Many Russians credit him 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.
"It's very clear that very many Russians have voted for Putin, but they've done so without the same enthusiasm they've had in the past," Al Jazeera's Jonah Hull said from Moscow.
"Either because they felt there was no viable choice, or because they had been convinced by the Kremlin rhetoric that Russia would crumble without him."
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.
Al Jazeera's Christopher True, reporting from Manezhnaya Square, the scene of the rally by Putin's supporters, said: "There is a mood of celebration here, with thousands of Russians enthusiastically hailing Putin's victory.
"However, circling the crowds, thousands of grim-faced riot police and other security forces are surrounding the Kremlin, apparently defending it from some unseen threat.
"Amid fears of an angry backlash from the opposition, Russia's government is making sure it is prepared for any eventualities."
Sunday's vote revealed the extent to which opposition to Putin remains fragmented, with none of his challengers other than Zyuganov, a perennial candidate in recent elections, managing to pick up any more than a few per cent of the vote.
The tycoon Mikhail Prokhorov had 7.0 per cent, slightly ahead of the populist Vladimir Zhirinovskyat 6.7 per cent, while the former upper house speaker Sergey Mironov may finish last with 3.7 per cent.
Russian officials attempted to counter allegations of vote rigging by installing two web cameras in each of the country's 90,000 polling stations, one showing the ballot box, the second showing election officials.
But Alexei Navalny, an opposition protest organiser and well-known blogger, alleged that "obvious and irrefutable" violations had taken place at polling stations, and said that vote counting was "neither fair nor truthful".
Golos, a Western-funded monitoring group, said it had already registered 2,283 reports of violations nationwide.
Election monitors from the Organisation for Security and Co-operation in Europe (OSCE) are due to report on the elections on Monday.
Lilia Shibanova, the executive director of the group, told Al Jazeera there had been "a lot of abuses" in Moscow, central Russia and Baskortostan.
"On the positive side, the web cameras and transparent ballot boxes have surely helped and it is the first time we have been able to monitor the elections in Chechnya, Dagestan and the Caucasus," she said.
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.