Thousands of Russians have rallied in Moscow and other cities to challenge Vladimir Putin's victory in Russia's presidential election, prompting hundreds of arrests.
Police said they had arrested 250 people in Moscow and 300 in Saint Petersburg on Monday after moving in roughly to break up demonstrations against what opposition activists say was a rigged vote.
About 20,000 anti-Putin protesters turned out in Pushkin Square in central Moscow chanting "Russia Yes! Putin No!".
The opposition supporters, who had been granted permission by authorities to protest for an hour, gathered in front of a stage emblazoned with the slogan "For fair elections".
Al Jazeera's Christopher True, reporting from the square, said: "After the allotted time for the demonstration was up, there was some heavy-handed tactics by police to clear the area.
"Officers formed rings and herded protesters down into the entrances of the Moscow metro. Dozens of people were arrested, including some of the main opposition leaders at the event."
Putin, who has dominated Russian politics since the beginning of the 21st century, won more than 63 per cent of Sunday's vote, according to the nearly complete official returns, but the opposition has alleged widespread fraud and independent monitors said the vote was skewed in Putin's favour.
Monitors from the Organisation for Security and Co-operation in Europe (OSCE) pointed at the lack of real competition in the race and said the vote count "was assessed negatively" in almost a third of polling stations observers visited.
Criticism of the vote has added fuel to protests by Putin's critics who are questioning his victory and demanding an end to his dominance of the Kremlin.
The Pushkin Square rally followed a series of massive previous demonstrations against Putin's rule. A protest planned by the opposition group, Solidarity, was stopped by riot police who bundled participants into waiting buses.
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.
Many of the protesters at Pushkin Square on Monday felt the election was unfair [Christopher True/Al Jazeera]
Police said that 15,000 people took part in a counter rally on Monday in support of Putin outside the Kremlin walls.
Al Jazeera's Jonah Hull, reporting earlier from Red Square adjoining the Kremlin, said the centre of Moscow was swarming with police and security services for the competing post-election rallies.
"Opposition protesters are saying that they reject the election result. They are rallying in Pushkin Square not too far from the Kremlin," he said.
"They were given permission just to rally for one hour and were then expected to disperse. The protesters have said they will try to form a human ring around the Kremlin."
Separately, police in Russia's second city, Saint Petersburg, arrested dozens of protesters demonstrating against Putin's poll victory, AFP reported.
Those arrested, including local deputies from the liberal Yabloko party, were among nearly 1,500 people who took part in a rally in the city centre that had not been sanctioned by the authorities, the correspondent said.
Meanwhile, Putin's nearest challenger in Sunday's vote said he would not congratulate his rival as the winner of the elections.
"I think that we must not congratulate Putin's team, him, or the country with this sort of election because everyone has lost, because the forced results and forced meetings cause nothing for the citizens of Russia except humiliation and distress," said Gennady Zyuganov, the leader of Russia's Communist party who came second in the vote with just over 17 per cent.
For all the allegations of voting irregularities, Putin's election win has not gone unrecognised.
Catherine Ashton, the European Union foreign affairs chief, acknowledged the "clear victory" for Putin.
"The EU takes note of the preliminary results of the presidential elections and the clear victory of Vladimir Putin," Ashton said in a statement which also called on Russia to address polling "shortcomings" identified by international observers.
The US State Department said it looked forward to working with Putin once election results are certified but urged the authorities to probe voting irregularities.
British Prime Minister David Cameron told Putin by phone that he would work with him to overcome differences between the two countries.
French President Nicolas Sarkozy congratulated Putin, while urging him to "continue democratic and economic modernisation."
Earlier French Foreign Minister Alain Juppe gave a cool reaction to Putin's return to the Russian presidency, saying the election "was not exemplary" but accepting that his controversial victory was not in doubt.