Vladimir Putin has won a third term as president, officials declared, after an election marred by allegations of widespread voter fraud.
Opposition figures said they were preparing huge demonstrations against the result in Moscow.
With 99% of ballots counted the United Russia leader won with almost 64% of the vote, election officials said.
Communist Gennady Zyuganov came second with around 17% of the vote.
Mikhail Prokhorov, a billionaire owner of an American basketball team, came in third, Nationalist Vladimir Zhirinovsky came fourth and socialist Sergei Mironov behind him. All three registered single digits in the poll.
Grigory Yavlinsky, leader of the liberal opposition Yabloko party, was not allowed to register for the election.
"I promised you we would win, and we won," Putin shouted to a flag-waving crowd of thousands of supporters outside the Kremlin on Sunday night, after claiming victory with just a quarter of votes counted.
Putin's eyes swam with tears, the AP reported, as he told his supporters that they had defeated those who wanted to "destroy" Russian statehood.
Outgoing president Dmitry Medvedev stood beside him as he said: "we showed that no one can direct us in anything!"
Putin, who served as prime minister between 2008 and 2012 after two terms as president, but has been widely seen as Russia's de facto leader since 2000 regardless of his official title, praised the elections as an "open and honest struggle".
But opponents disputed the landslide results, and said that there was evidence of widespread fraud, intimidation and ballot-box stuffing.
Despite Putin's strong support among many in Russia, who see him as a guardian of stability, the opposition had hoped to push him into a second round of voting.
Russian independent election watchdog Golos said there had been widespread claims of "carousel voting" in which voters were bused to different poll stations to vote multiple times.
At one polling station in Dagestan, near Chechnya, web cams showed Putin supporters throwing ballot after ballot into boxes.
The Central Election Commission responded by saying the results from that station would not be valid.
In some stations near Dagestan Putin received more than 90% of the vote.
"These elections are not free. ... That's why we'll have protests tomorrow," said opposition politician Mikhail Kasyanov, who was Putin's first prime minister.
"We will not recognise the president as legitimate," he said.
The claims echo those made in December after independent observers said parliamentary elections had been tainted by a number of violations.
Those allegations sparked a wave of protests, seen by many as posing the first serious threat to Putin's authority for more than a decade.
Fresh demonstrations against the election result are expected in Moscow on Monday. On Sunday evening a woman was arrested after she stropped to his waist and revealed the word "thief" written on her body, the AP said.
Putin's campaign chief, Stanislav Govorukhin, said the claims of fraud were "ridiculous."
The UK Foreign Office said it was waiting "with interest" for reports from the Organisation for Security and Co-operation in Europe (OSCE) and the Office for Democratic Institutions and Human Rights (ODIHR), which are due at around 2pm on Monday.
A spokesman said: "We fully support the important democratic elections in Russia as elsewhere in the world.
"As a Council of Europe member state Russia has an obligation to uphold key democratic norms and standards."
Former foreign secretary David Miliband branded Putin a "ruthless" dictator whose days are numbered.
In an article for The Sun he warned it would be wrong to underestimate the "intelligent" leader but predicted he will not survive a six-year term at the Kremlin.
Miliband wrote: "It is wrong to underestimate Putin. He is intelligent, worldly and ruthless."
Relations between Britain and Russia reached breaking point after the murder in London of dissident critic Alexander Litvinenko but have been more cordial since Prime Minister David Cameron's visit to the nation last year.
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