Radical opposition activist Sergei Udaltsov will meet the new year in a Moscow prison, a city judge decreed in a ruling that sparked protests outside the courtroom.

The new 10-day jail term for Udaltsov appeared to be a bad political move, fueling anti-Kremlin sentiment that is still riding high after a record protest rally on Prospekt Akademika Sakharova last weekend.

The Kremlin, which earlier made token concessions to protesters, had no comment on Udaltsov's plight. Meanwhile, bloggers launched a campaign against the judge who jailed him, and about 1,500 signed up on Facebook for a rally to demand his release.

Judge Olga Borovkova passed sentence on Udaltsov late Sunday, shortly after he was released from nearly month-long detention, part of which he spent in the hospital. It was his 14th arrest in 2011.

Borovkova found Udaltsov guilty of resisting police during a one-man picket near the office of the Central Elections Commission in October. She dismissed the defense's claim that such pickets require no permission from authorities, as well as video footage that showed Udaltsov offering no resistance during arrest.

Several hundreds of protesters rallied outside the court building on Sunday. Inside, dozens of reporters and Udaltsov's supporters protested the judge's decision to expel them from the courtroom, unsuccessfully trying to force their way in past security guards.

Protesters chanted "Borovkova is a servant of Satan," "Freedom to Seryoga" and "Shame on the corrupt court," a video uploaded on YouTube showed.

The police only detained one protester, environmental activist Yaroslav Nikitenko, who was also slapped with 10 days in jail for participating in an unsanctioned rally.

Udaltsov has repeatedly staged hunger strikes over his recent detentions, ending up in intensive care earlier this month.

He said Monday that doctors have convinced him to start taking food again to avoid possibly life-threatening health problems.

"They told me that I need serious treatment now. Of course, a hunger strike is simply not acceptable in such a situation because it can result in a bleeding," Udaltsov told Dozhd television.

He spoke by telephone from a hospital, where he was brought straight from the courtroom. He said he would remain there at least until Wednesday, after which he would be transferred back to his prison cell.

His lawyers have filed an appeal, which is to be reviewed Tuesday by judge Alexei Krivoruchko, notorious for being on the "Magnitsky list" of 60 officials implicated in the death of Hermitage Capital lawyer Sergei Magnitsky. Back in 2009, Krivoruchko ordered Magnitsky to be held in pretrial detention despite the lawyer's health problems. Magnitsky died days after the ruling.

Judge Borovkova, despite her young age of 26, has also earned notoriety among the opposition, whose leaders she has often sentenced to short prison terms despite shaky evidence of wrongdoing.

Her phone number and home address, along with calls to harass her, were leaked to blogs Monday, though many bloggers dismissed it as provocation and called instead for a legal crackdown on Borovkova.

Court officials reported that Udaltsov's ally Ilya Ponomaryov, a State Duma deputy with A Just Russia, had eaten several pages out of Udaltsov's criminal case records.

When Udaltsov's lawyer passed Ponomaryov several pages from the case in the courtroom, the legislator "tore them into pieces" and "ate" them, a court source told Interfax on condition of anonymity. Ponomaryov denied wrongdoing.

Udaltsov, 34, a native Muscovite, took up politics in the 1990s, when his family of intelligentsia had fallen on hard times following the Soviet Union's demise. In 1998, he created his first political group, Red Youth Vanguard, allied with radical Communist leader Viktor Anpilov, and he proceeded to become co-founder of the Left Front group, which collaborated with The Other Russia coalition in the mid-to-late 2000s. He also co-established in 2009 the still-unregistered Rot Front party.

Udaltsov's new sentence has prompted sympathy for him even in the pro-Kremlin camp. Margarita Simonyan, head of state-owned Russia Today television and a vehement opposition-basher, wrote on her Twitter late Sunday that she supports Udaltsov "out of simple humanism."

Udaltsov's new arrest is the authorities' real response to this month's protest rallies, the biggest of their kind since 1993, Kommersant reporter Oleg Kashin wrote in the Dewarist community on LiveJournal.

Tens of thousands rallied on Moscow's Bolotnaya Ploshchad and Prospekt Akademika Sakharova against the Kremlin and alleged vote-rigging in the Dec. 4 parliamentary elections. Resolutions at both rallies included demands for repeat elections and punishment for officials implicated in vote-rigging, as well as for the release of "political prisoners," starting with Udaltsov.

"Through the new, demonstrative and brazen arrest for Udaltsov, the authorities have reacted to this demand," Kashin wrote. "Now the question for you, who chanted 'all for one and one for all,' is, how would you respond to authorities?"

Between 100 and 300 people, including whistleblower Alexei Navalny, rallied again by the Tverskoi District Court late Monday, with no detentions reported.

About 1,500 signed up for a sanctioned rally in Udaltsov's support on Pushkin Square on Thursday — admittedly a far cry from the 50,000-plus who reported on Facebook attending the Saturday rally on Prospekt Akademika Sakharova.