Moscow: Russian President Dmitry Medvedev on Sunday ordered a probe into allegations of vote rigging that sparked the biggest anti-government agitation in post-Soviet Russia by tens of thousands of protestors who called for an end to Prime Minister Vladimir Putin's rule.

"I don't agree either with slogans nor statements made at the rallies. All the same I have issued orders to probe all the information concerning the observance of electoral law at the polling stations," Medvedev wrote on his Facebook status.

Calling for fair elections in the wake of last weekend's parliamentary polls, allegedly rigged in favour of the ruling Russia United party of Putin, some 50,000 Russians on Saturday took to the streets demanding an end to Putin's 'managed democracy'.

Commenting on yesterday's protest rallies, largest of which was held at Bolotnya Square near the Kremlin, Medvedev noted that under the Russian constitution the people have freedom of speech and gathering in public.

"People have right to express their views, which they did Saturday. Its good that everything proceeded within the framework of law," Medvedev wrote in his Facebook blog.

The protests come three months before the Russian strongman, who was president in 2000-2008 and effectively remained incharge of the country's while prime minister, will seek a third presidential term.

Last Sunday's Parliamentary election for lower house Duma signalled the end of Putin's honeymoon with Russia. Putin's 'United Russia' lost its overwhelming majority of 315 seats in the 450-strong lower house, but retained 238 seats allegedly due to mass-scale ballot-rigging.

Facing rare street demonstrations against his rule, Putin on Tuesday accused the US of instigating post-election protests in Russia that are posing a challenge to his authority. Medvedev's decision to launch a probe into alleged vote fraud came amid fresh protest demonstrations in Urals city of Perm, Siberian cities of Novosibirsk and Omsk on Sunday.

Russia's Public Chamber - a buffer between the regime and the civil society - in a statement appealed to the country's leaders to heed the voice of protestors, who represent the
cross section of the Russian society.

"Opposition rallies against recent elections that culminated in a massive demonstration in Moscow this weekend are a major "watershed" in Russia's post-Soviet social and political development that the country's leadership must reckon with," state-run RIA Novosti quoted analysts as saying.

"The rally in Moscow on Saturday, attended by tens of thousands of relatively young, well-dressed, educated "mainstream" people rather than a few hundred marginal politicians and their followers, demonstrated that average Russian people in large numbers have real questions for the country's leadership," it said.

"They (protesters) are not interested in burning down the state but rather in making their voices heard. And this, political experts say, is a force that Prime Minister Vladimir Putin, President Dmitry Medvedev and other top Russian leaders cannot afford to ignore," the agency, considered as the voice of the Russian government, underscored in its comments.

The protesters' main demand, which united representatives of the entire political spectrum, was a review of the results of the elections.

In the controversial December 4 Duma election, the ruling United Russia party got 49.32 percent of the votes, the Communist Party 19.19 percent, A Just Russia party 13.24 percent, the LDPR 11.67 percent, Yabloko 3.43 percent, Patriots of Russia 0.97 percent and the Right Cause party 0. 6 percent.

The opposition, including opposition factions in Parliament, believes that the official electoral data were falsified and that the day of voting itself was marked by alleged massive breaches of electoral legislation, including ballot stuffing and the removal of observers from polling stations.

The report said that for the first time in Russia's political history, massive protests were coordinated outside traditional political structures, using social networks where people independently organised groups.

RIA Novosti said a mere look at the participants of the rally in Moscow showed that the protests was staged not by social groups who are regularly angry at the government - pensioners and low-paid workers.

The protesters were "educated and relatively 'well-to-do' young professionals who have as much interest as the country's leaders in seeing stable social, economic and political development but who have, until now, lacked any organized political force".