Russian protestors who shook the authorities with mass protests against the rule of Vladimir Putin are set to hold a new rally Thursday against the detention of a prominent left-wing activist.

More than 2,000 people have vowed on social media network Facebook to attend the rally in Pushkin Square in central Moscow which has not been authorised by the municipal authorities.

The rally was called after a Moscow court late Sunday ordered the detention of left-wing activist Sergei Udaltsov for 10 days despite growing alarm for his frail health after he went on hunger strike.

The meeting is expected to be nowhere near the size of last Saturday's mass rally against allegedly rigged elections and Putin's domination of Russia which brought tens of thousands onto the streets.

But it is expected to reflect genuine anger over the detention of Udaltsov. Organisers are hoping that there will be no new confrontation with the security forces, despite the lack of authorisation.

Their Facebook page is now calling the event a "gathering for the freedom and life of Udaltsov and other political prisoners" rather than a protest in a bid not to provoke the police. But it is also calling for a "mass" turnout.

"This format of meeting does not require prior agreement from the police," claimed lawmaker Ilya Ponomaryov, a member of the opposition A Just Russia party, saying that the municipality refused to authorise a protest.

"We do not want there to be excesses or any arrests just before the New Year," he told Kommersant FM radio, adding that the demonstrators were being asked not to bring banners with them.

While Udaltsov's radical left-wing views are not shared by all in the anti-Putin protest movement, his plight has become a rallying cause for the opposition angered by the harsh behaviour of the Moscow courts.

Udaltsov had already served a fortnight sentence for taking part in a protest after the December 4 parliamentary elections and his extra 10-day term was part of a punishment dating back to October he had not served out.

There is particular anger among the opposition over the strict rulings of Moscow's Tverskoi district court magistrate Olga Borovkova who sentenced Udaltsov and a number of other prominent opposition protestors this month.

The Vedomosti daily recalled that it was Borovkova who had forced opposition leader Boris Nemstov to stand for several hours during a case in January and she also jailed protest movement leaders Alexei Navalny and Ilya Yashin to 15 day terms for taking part in post-election protests.

Udaltsov has been sentenced to three short successive prison terms in recent weeks with the result that he has spent most of the past month in jail. He is currently in hospital but under permanent guard.

"Udaltsov had to go on hunger strike simply because they were terrorising him," Navalny wrote on his Live Journal blog.

The leaders of the protest movement have not yet said when the next mass demonstration will take place but they have indicated it will not be before the end of the New Year holidays in mid-January.

The protest wave has posed a significant challenge for Putin's 12 year dominance of Russia as he prepares to stand for a third term as president in March elections after his four year stint as prime minister.