In what has been called the largest ever showing of anti-government protest in post-Soviet Russia, tens of thousands gathered across the country Saturday — with a massive demonstration in Moscow — to rally against alleged election fraud.

Demonstrations were held in more than 60 cities and much of the public anger is being directed at Prime Minister Vladimir Putin and the ruling United Russia Party. There were fewer than 100 arrests nation-wide, indicating a surprising show of restraint by police.

The independent Russian election-observer group Golos said Saturday the "[United Russia Party had] achieved the majority mandate by falsification," confirming what opposition activists and independent monitors had already alleged as widespread fraud in last weekend's parliamentary elections. Demonstrators want the government to nullify those results and hold fresh elections. 

Exact figures on the turnout were nearly impossible to confirm. Police said 25,000 amassed in a Moscow square while some protest organizers put the figure as high as 150,000.

At least 50,000 officers and riot troops were deployed in the city ahead of the demonstrations, the BBC reported. However, police appeared content to remain on the sidelines. Elsewhere in Russia, an estimated 7,000 protesters assembled in St. Petersburg, and demonstrations ranging from a few hundred people to a thousand were held in other locales.

"You can see thousands … of people peacefully protesting what they are calling ballot stuffing and vote rigging," Jessica Golloher, a correspondent with GRN, told CBC News from Moscow.

Putin, who was the president of Russia in 2000-2008 before stepping aside because of term limits, will seek a new term in the Kremlin in the March presidential elections. The protests have tarnished his campaign, but there is not yet any obvious strong challenger.

A statement released late Saturday by Putin's press secretary, Dmitry Peskov, acknowledged the day's protests by people "displeased" with the elections but noted demonstrations in support of the elections in recent days.

"We respect the point of view of the protesters, we are hearing what is being said, and we will continue to listen to them," the statement said. "The citizens of Russia have a right to express their point of view, in protest and in support, and those rights will continue to be secured as long as all sides do so in a lawful and peaceful manner."

The crowds included both the young and old with demonstrators chanting slogans, waving flags and carrying placards. The turnout was enough to draw the attention of the country's state-controlled media, which normally ignores the opposition. The protests received a significant amount of air-time.

A top United Russia official, Andrei Isayev, acknowledged late Saturday that "expression of this point of view is extremely important and will be heard in the mass media, society and the state."

'Forced to protest'

The demonstrations come three months before Putin, who was president from 2000-2008 and effectively remained the country's leader while prime minister, is to seek a third term in office. The public outpouring challenges his image, supported by state-controlled TV channels, as a man who won the affection of most Russians.

That image was undercut by parliamentary elections on Dec. 4, during which his United Party narrowly retained a majority of seats — despite opposition claims of fraud — but lost the unassailable two-thirds majority it held in the previous parliament.

"A lot of people that I've spoken with basically say that they want Vladimir Putin out of the country," Golloher said. "They don't want him to rule Russia anymore."

Others at the protest said they want more democratic freedoms.

"I don't think any citizen of the country can say he is very happy with anything. We don't have an independent judiciary, there is no freedom of expression — all this combined creates a situation where people are forced to protest," said demonstrator Albert Yusupov.

Several hundred demonstrators gathered in the Pacific city of Vladivostok shouting "Putin's a louse." The Interfax news agency reported that about 15 people were arrested at a protest in the Siberian city of Perm and about 30 were arrested in the eastern city of Khabarovsk when a flash mob started an unauthorized protest.

Officials sanction rallies

In an unusual move, government officials gave the go-ahead for many of the demonstrations, including allowing 30,000 to attend the rally in Moscow.

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But in what appeared to be an attempt to prevent young people from attending in the capital, the city's school system declared Saturday afternoon a mandatory extra school day for grades nine through 11. 

Russian President Dmitry Medvedev conceded this week that election law may have been violated. In another rare move, Putin suggested "dialogue with the opposition-minded." 

The Kremlin has come under strong international pressure, with U.S. Secretary of State Hillary Clinton calling the vote unfair and urging an investigation into fraud. Putin in turn criticized Clinton and the United States for allegedly instigating protests and trying to undermine Russia. Hundreds of people were arrested in smaller protests earlier in the week, including several prominent opposition activists.

Calls for follow-up protests

Although U.S. Sen. John McCain recently warned Putin through Twitter that an Arab Spring-type movement was coming to the country, many commentators have questioned whether Russian activists can sustain a prolonged demonstration similar to the one that ousted Egypt's Hosni Mubarak.

"It's not clear whether or not it will have legs," Julia Ioffe from Foreign Policy magazine told CBC News.

However, the rally in Moscow was a noticeable increase in the number of people willing to voice their opposition to perceived wrongs, she added. Activists are also calling for follow-up demonstrations on Dec. 17 and 24.

Russian police are unlikely to tolerate long-term occupations of public areas and staged events at regular intervals may be less effective at pushing for change. 

Russia's opposition is also vulnerable to attacks on the websites and social media that have nourished other protests. This week, an official of Vkontakte, a Russian version of Facebook, reported pressure from the FSB, the KGB's main successor, to block access to opposition groups, but said his company refused.

On election day, the websites of a main independent radio station and the country's only independent election-monitoring group fell victim to denial-of-service hacker attacks.

Still, Ioffe said the large turnout Saturday will likely put pressure on the government to make some concessions.

With files from The Associated Press