More than 50,000 people took to the streets of Moscow today as opposition forces challenge Vladamir Putin's government in a new wave of protests against alleged election fraud.

Organisers of the demonstration hope it will be as large as a protest two weeks ago that drew tens of thousands - the largest show of discontent since the 1991 Soviet collapse - although rallies in other cities in the far east and Siberia earlier today drew much smaller crowds.

Rally participants began gathering on a broad avenue about 2.5 kilometres from the Kremlin on a snowy day. Nearly 53,000 people have so far signed up on Facebook to take part.

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Turnout: Tens of thousands of demonstrators rally in the Russian capital in what is believed to be the largest protest so far against election fraud
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Ridicule: As thousands take to the streets of Moscow in protest, a placard shows Russian Prime Minister Vladimir Putin draped in a condom in reference to remarks he made mistaking white ribbons worn by protesters for contraceptives

A stage at one side of the 700-meter (0.43 mile) avenue featured placards reading 'Russia Will be Free' and 'This Election is a Farce'.

'We want to back those who are fighting for our rights,' said 16-year-old Darya Andryukhina, who said she also attended the previous rally.

'People have come here because they want respect,' said Tamara Voronina, 54, who said she was proud of her three sons who had also joined the protest.

Recent protests in Moscow and other cities have dented Prime Minister Vladimir Putin's authority as he seeks to reclaim the presidency in next March's vote. The Kremlin has responded by promising a set of political reforms that would liberalize election rules.

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Outnumbered: A policeman struggles to escape from the clutches of angry demonstrators at the start of today's protest against election results
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Outcry: Demonstrators hold placards with slogans such as 'Russia Will be Free' and 'This Election is a Farce'
But protest leaders say they will continue pushing for a rerun of the Dec. 4 parliamentary election and punishment for officials accused of fraud. They say maintaining momentum is key to forcing the government to accept their demands.

The protests have reflected a growing public frustration with Putin, who ruled Russia as president in 2000-2008, and has remained the nation's No. 1 leader after moving into the premier's seat due to a constitutional term limit.

Putin has accused the U.S. of fomenting the protests in order to weaken Russia and said, sarcastically, that he thought the white ribbons many protesters wear as an emblem were condoms.

In a response to Putin's blustery rhetoric, one protester Saturday held a picture montage of Putin with his head wrapped in a condom like a grandmother's headscarf. Another one held a sign saying: 'Hillary, I'm still Waiting for My Money,' referring to U.S. Sec. of State Hillary Clinton.

Although he derided the demonstrators as Western stooges, Putin has also sought to soothe public anger by promising to relax his grip on the nation's political scene.

He has promised to liberalize registration rules for opposition parties and restore the direct election of governors he abolished in 2004.

Putin's stand-in President Dmitry Medvedev spelled out those and other proposed changes in Thursday's state-of-the nation address, promising to restore single-ballot elections to fill half of the seats in parliament and ease rules for the presidential election.

Some opposition leaders welcomed the proposals, but stressed the need for the protests to continue to force the Kremlin to quickly turn promises into law.

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© Maria Pleshkova / Demotix
A member of the anti-vote rigging flashmob confronts two police officers in central Moscow
The electoral changes, however, will only apply to a new election cycle years away, and the opposition has stressed the need to focus on preventing fraud in the presidential election and mounting a consolidated challenge to Putin in the March vote.

In another sign of authorities' efforts to stem a tide of public anger, the presidential human rights commission early Saturday issued a statement condemning violations in the vote and backing protesters' calls for the ouster of Central Election Commission chief Vladimir Churov.

It said that allegations of widespread fraud have led to a 'moral and political discreditation of the election system and the lower house of parliament, creating a real threat to the Russian state.'