Russia's opposition on Saturday started to mass for a new protest against the alleged rigging of parliamentary polls expected to attract tens of thousands of people in a new challenge to Vladimir Putin.
Hundreds of people, clutching white balloons and banners with the slogan "For Free Elections" were already gathering in central Moscow ahead of the start of the protest, an AFP correspondent reported.
In an unexpected boost to the protestors, an advisory Kremlin rights panel said in a statement that the new parliament had been discredited by the accusations of fraud and fresh elections should be called.
President Dmitry Medvedev this week announced reforms to appease the protestors -- including resuming elections for regional governors -- but the changes fell far short of their demands for a re-run of the legislative polls.
Around 100 people took part in a protest in the Far Eastern city of Vladivostok, an AFP correspondent said, and other rallies were under way in Siberia. But by far the biggest protest is awaited in the Russian capital.
Over 50,000 people have now vowed on Facebook to attend the protest starting at 1000 GMT on a Moscow avenue named after the Soviet dissident Andrei Sakharov with the slogan "a meeting for free elections."
Incensed by claims of wholesale violations in the polls that handed a reduced majority to prime minister Putin's United Russia, tens of thousands of people already took to the streets across Russia on December 10.
Those protests were the biggest show of public anger in Russia since the chaotic 1990s and the first sign of a growing challenge to Putin's 12-year domination of the country.
However the mass protests have been sanctioned by the authorities, in a major turnaround by the police who arrested hundreds of people who took part in demonstrations in the immediate aftermath of the elections.
Among those attending in Moscow may be the Soviet Union's last leader Mikhail Gorbachev, 80, who has been virulently critical of the elections, although his spokesman emphasised it would depend on how he felt.
Gorbachev said in an interview with the Novaya Gazeta on Friday that he was ashamed by Putin's reaction to the protests, after the Russian strongman compared the white ribbons worn by demonstrators to condoms.
Charismatic anti-Kremlin blogger Alexei Navalny was also expected to be present after his release from prison following a brief sentence for his participation in a protest shortly after the elections.
Former finance minister Alexei Kudrin said he would address the rally after publishing an open letter telling the protestors he shared "your negative emotions about the results of the parliamentary polls in our country."
The advisory Kremlin rights panel said on the eve of the protest that the reported violations discredited parliament and had led to the "distrust of the poll results."
"This discredits the electoral system and the lower house of parliament and... creates a real threat to the Russian state," it said in a statement, calling for the resignation of election commission chief Vladimir Churov.
It said that new election laws should be put in place "with the aim of then calling snap elections" to replace the current parliament.
But the commission dismissed the call for Churov to resign, with its member Yelena Dubrovina telling the Interfax news agency that "this decision does not have any legal, judicial consequences."
Defying the protests, the newly elected lower house of parliament, the State Duma, held its first session on Wednesday.
The ruling United Russia party won less than half the vote in the elections and lost 77 seats as fatigue set in with the rule of Putin, who is planning to win his old Kremlin job back in March polls and could stay in power until 2024.
But the opposition says the party's performance would have been even worse in free elections.