Moscow: The Russian capital witnessed its biggest mass protest in years as thousands of people took to streets shouting anti-Putin slogans, challenging the outcome of Sunday's Duma polls that were marred by allegations of irregularities.

The parliamentary election were won by Prime Minister Vladmir Putin's United Russia party albeit by a reduced margin, but the results, being considered rigged by many, seem to have sparked the biggest ever anti-Putin wave.

The rally allowed by city authorities in downtown Moscow, outside the Chistiye Prudi metro station, last night turned into a mass protest against Putin and his party.

According to various claims, from 2,000 to 10,000 people had gathered at the rally in the biggest mass protest over a decade, carrying placards that read 'Down with the Party of Swindlers and Thieves!'

Hundreds of people carrying identical red whistles were blowing them to 'whistle out Putin' and chanting 'Russia without Putin'.

The state-controlled TV channels completely blacked out the news of the massive anti-Putin protests in Moscow and his own hometown St Petersburg, amid reports of widespread ballot rigging.

According to liberal websites the police arrested at least 300 people including the influential whistleblower against rampant corruption in the government Alexei Navalny.

"I know Alexei that you are right, but you are not allowed to do this," a police officer detaining Navalny was quoted as saying by a blogger on the Echo Moskvy liberal radio's website.

The claim of ballot rigging has been supported by the opposition parties, although they have doubled their presence in the newly-elected house after United Russia retained its simple majority though it lost 87 seats.

About 120 people were also detained at a protest in St Petersburg - the hometown both Putin and President Dmitry Medvedev.

Protesters trying to march towards the Central Election Commission were urging the police to "side with the people" and allow them to move ahead, before they were finally dispersed at Lubyanka Square near the FSB headquarters.

As per the media report, Sunday's elections were marred by widespread allegations of poll procedure in favour of United Russia, with dozens of video clips appearing to show election fraud uploaded onto the Internet.

International observers from the Council of Europe and the Organisation for Security and Co-operation in Europe have reported "flagrant procedural violations," including cases of ballot-stuffing.

The liberal anti-Kremlin opposition leader Vladimir Milov said: "Now nobody can say that the whole country loves Putin."

Putin is seeking a return to the Kremlin after March 2012 elections under a job swap deal with incumbent Medvedev.    

"The best thing would be to suggest Putin to get off the train, which he will not do: But there is a need to work out an exit strategy to shift genuine democracy," Evgeny
Gontmakher of pro-Medvedev Institute of Development of Modern Russia (INSOR) wrote in his blog.

(Agencies)