MOSCOW — Sergei Udaltsov, a Russian opposition leader, was detained and interrogated for several hours Wednesday by authorities investigating whether he and colleagues were plotting to organize mass disturbances.
Udaltsov was eventually released, investigators said, based on a pledge that he not leave Moscow until the investigation has concluded.
The inquiry, the latest sign of a Kremlin crackdown on opposition advocates, was launched this month after NTV, a government-friendly television network, aired a documentary in which Udaltsov and associates allegedly discussed organizing mass disorder and seizing power in some Russian cities.
Emerging from the interrogation late at night, Udaltsov called such accusations "political vengeance of the Kremlin" and called the NTV film "a dirty and cheap manipulation." He also denied talking with a Georgian official about funding for the Russian protest movement.
"The Kremlin took advantage of the current pause in our movement and immediately dealt its strike, interpreting our temporary slowing down as a sign of weakness," Udaltsov said in a phone interview shortly after his release. "Our only way to retaliate is to step up protest activities as soon as possible."
Vladimir Markin, a spokesman for the Russian Investigative Committee, indicated that Udaltsov could face serious criminal charges.
Markin issued a warning to "those who think that in our country one can with impunity engage in organizing mass disorders, prepare terrorist and other actions endangering the life and health of Russian citizens." Speaking on Russia-24, a TV news network, he said, "You are underestimating the professionalism of the Russian special services and have poor knowledge of the Russian Criminal Code, which provides for punishment that includes a life sentence."
Udaltsov, a key organizer of mass street protests in Moscow and other cities against President Vladimir Putin and the ruling United Russia party, could face up to 10 years of imprisonment if charged and convicted of conspiring to organize mass disorders. If found guilty of high treason, a serious charge implied by Markin, Udaltsov could face a life sentence.
Givi Targamadze, the Georgian parliament defense and security committee chief named by NTV as a participant in the alleged meeting, denied in an interview with the newspaper Novaya Gazeta ever meeting Udaltsov.
Masked law enforcement agents searched the apartments of Udaltsov and some of his associates Wednesday. Konstantin Lebedev, Udaltsov's aide, was also detained and will remain in custody for 48 hours, officials said.
Human rights activists say the Kremlin has stepped up questionable attacks on opponents as a result of the mass protests that shook Russia after December parliamentary elections and the March vote that returned Putin to the presidential office for a third term.
"Putin and his men are trying to scare the opposition stiff by intensifying repression, but I think such shortsighted actions will give a new surge to the opposition movement," Lev Ponomarev, head of the For Human Rights organization, said in an interview.
The investigative committee is preparing to send to court a case against 17 opposition activists charged with clashing with police in Moscow on May 6, the eve of Putin's inauguration. The protest march ended in violent clashes that left dozens of demonstrators and some policemen injured.
The committee has also accused several opposition leaders of embezzlement.
"The whole show is like the farce repetition of the infamous operations conducted by the Soviet KGB against dissidents, but to give them credit, the KGB was much more refined and professional in their approach," opposition leader Gennady Gudkov said in an interview.