In unprecedented scenes, thousands of Russians gathered in the streets Monday night, accusing Prime Minister Vladimir Putin's party of manipulating this weekend's parliamentary election.

As they shouted "Russia without Putin," the protesters, mainly young men, denounced the vote as shameful. But they were met by baton-wielding riot police as they attempted to march toward the Central Elections Commissions, near the Kremlin. Some were beaten over the head, while others were dragged into waiting trucks

In the biggest opposition rally in years, the police detained about 300 activists. The number of protesters ranged from 5,000 to 10,000 according to the AP.

In St. Petersburg, the authorities detained about 120 people.

Putin's United Russia party won about 50 per cent of Sunday's reported vote, which represent a sharp drop from the last election, when the party took 64 per cent.

The opposition politicians and monitors accused Putin of fraud at the ballot box in order to inflate the vote's results, which represent a symbolic blow to United Russia.

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The Organisation for Security and Co-Operation in Europe denounced some problems with the counting process. "The contest was also slanted in favour of the ruling party, the election administration lacked independence, most media were partial and state authorities interfered unduly at different levels," said Petros Efthymiou.

U.S. Secretary of State Hillary Clinton also expressed "serious concerns" about the conduct of election.

Amnesty International firmly condemned the arrests of protesters. "These disgraceful detentions highlight once again the failure of the Russian government to respect its citizens' rights to freedom of expression and assembly," said Nicola Duckworth, director of Amnesty International's Europe and Central Asia Programme.

"The vast majority of those arrested since Sunday have sought merely to peacefully express their protest. They are prisoners of conscience and they must be released immediately."

Several opposition activists were detained at home or on their way to demonstrations, with some being sentenced to up to 10 days of administrative detention, according to Amnesty International.

Among the opposition politicians detained is Andrei Gorin from the Other Russia, who was reportedly beaten and sentenced to 10 days' administrative detention.

Fury has been growing inside Russia since Putin, currently the prime minister, announced his intention to run for the presidency in 2012. While the vote on Sunday provided the first real sign of Russians' dissatisfaction with the former president, some hints were already present months ago. In November, the International Business Times broke the news that Putin was greeted with whistles and boos on live television as he congratulated Russian heavyweight champion Fedor Emelianenko after beating American Jeff Monson.

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Observers said it was the first time Putin had been publicly booed. Russian television edited the footage to remove the booing, but viewers uploaded the television footage on YouTube, where it had gone viral, reaching 500,000 hits as of Monday morning. The news about Putin getting booed was the top news in the rating by the country's major online search engine Yandex as of Monday morning, according to the RIA Novosti news service.

Blogger Alexei Navalny posted the video on his site and wrote that it was "the end of an era" for the Russian leader, a judo black belt and a fan of martial arts.