Opposition leader Sergei Udaltsov (left) is escorted from his apartment after being detained in Moscow on Oct. 17, 2012. Russian authorities launched criminal proceedings against opposition leader Sergei Udaltsov on Wednesday, accusing him of planning "mass disorder" in protests against President Vladimir Putin's 12-year rule. (MAXIM SHEMETOV/REUTERS)

Opposition leader Sergei Udaltsov was charged Friday with plotting mass disorder, part of a clampdown by Russian authorities on public dissent, but was unexpectedly allowed to remain free on his own recognizance.

The decision to release him surprised Udaltsov, a 35-year-old socialist, and his attorney, who had predicted Udaltsov would join two associates in jail.

One supporter suggested that the authorities were hoping Udaltsov would flee the country, which would discredit him and deprive his Left Front bloc of its leadership. If convicted of plotting mass disorder, he would face up to 10 years in prison.

Udaltsov and the other two activists were accused based on allegations contained in a documentary that was broadcast Oct. 5 on a Kremlin-friendly television station.

One of the jailed associates, Leonid Razvozzhayev, said he was abducted last week in Ukraine, where he was asking a U.N. refugee agency for asylum. He said he was spirited into Russia, bound and chained, and threatened and deprived of food and water until he signed a confession. He disavowed the confession Thursday, as soon as he saw a lawyer.

The Ukrainian Security Service said in a statement Friday that it was investigating Razvozzhayev’s claim, which has attracted the attention of the U.N. High Commissioner for Refugees, European officials and the United States.

“We are quite concerned about allegations that he was forced to confess, that he may have been subjected to torture,” State Department spokeswoman Victoria Nuland said in Washington. She said the United States is also uncomfortable with Russia’s investigation of a number of activists who took part in a May 6 demonstration, on the eve of Vladimir Putin’s inauguration as president.

“We have shared our concerns with the Russian government, including about the Razvozzhayev case,” Nuland said.

Analysts say Udaltsov’s arrest is part of a crackdown on organizers of the street protests that began in Russia in December over allegations of rigged parliamentary elections. Udaltsov and his Left Front forces are vulnerable to prosecution, these experts say, because of their heated rhetoric and because the world community may be less sympathetic to them than to more mainstream, liberal opposition groups.

Udaltsov opposes capitalism and private ownership of property. Still, liberals have rallied around him since he came under investigation, asserting that he is guilty of nothing more than holding opinions unpopular with Russian officials.

“What is happening is the beginning of a large-scale, long-planned process to persecute dissent and public disagreement,” Lyudmila Alexeyeva, a human rights activist and chairwoman of the Moscow Helsinki Group, told the Interfax news agency Friday. “They will get everyone.”

Indeed, Gennady Gudkov, a more liberal opposition leader, recently was forced out of the lower house of parliament after authorities accused him of operating a business in violation of parliamentary rules.

Udaltsov, who says he is innocent, said he had been followed constantly since he was informed Oct. 17 that he was under investigation. But Alexei Sakhnin, a Left Front member, said Friday that the constant shadowing had suddenly stopped, as if a sign to Udaltsov to run. Udaltsov said investigators told him that his freedom was not permanent and that he could be picked up at any time.

“If anyone expected me to flee,” Udaltsov said, “they were mistaken. I will bear it all, and I hope those who support me will not be silent or give in.”