Updated

Russia's top investigative agency filed criminal charges Thursday against an opposition leader's assistant, continuing a widespread crackdown on the movement against President Vladimir Putin.

The Investigative Committee said in a statement that Left Front member Konstantin Lebedev has been charged with plotting mass riots and could face a jail term of up to 10 years.

Investigators said the 33-year-old Lebedev, who has been in custody since Wednesday, denied the charges and has refused to give evidence. A court sanctioned his arrest Thursday.

On Wednesday, officials interrogated Lebedev's boss, Sergei Udaltsov, who is also a suspect, and searched his home before releasing him on the condition that he not leave Moscow.

Investigators are relying on hidden camera footage aired earlier this month by a Kremlin-friendly TV channel. The documentary claimed that Udaltsov met with officials from the neighboring nation of Georgia to raise money, partly from disgraced banker Andrei Borodin, to overthrow Putin's government by sending communists and neo-fascists to seize the Kremlin as well as several Russian cities.

Investigators said that Udaltsov, Lebedev and another leftist activist who remained at large, Leonid Razvozhayev, are suspected of planning to stage mass riots involving the use of firearms, ransacking and arson in Moscow, Kaliningrad, Vladivostok and other cities.

Udaltsov, a shaven-headed communist firebrand who wore a Joseph Stalin T-shirt to his own wedding, has called the documentary "filth" and said the charges are revenge for his political activity. He insisted that the TV footage, in which the figure purported to be him is nearly always out of focus, was doctored.

Both Udaltsov and Givi Targamadze, the senior Georgian lawmaker that Russian officials say is behind the plot, deny ever meeting each other.

"I think that one thing is really evident: the goal to arrest Udaltsov was set, and in order to achieve it this film or program was fabricated," Targamadze, who heads the Georgian parliament's defense and security committee, told The Associated Press on Thursday in the Georgian capital, Tbilisi.

"I think the one thing is really evident, that the aim to arrest Udaltsov was set first and in order to achieve that goal this film or program has been fabricated," Targamadze, who heads the Georgian parliament's defense and security committee, told The Associated Press in the Georgian capital, Tbilisi.

Russian investigators said they had carefully studied the footage and concluded it was genuine.

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Misha Dzhindzhikhashvili contributed to this report from Tbilisi, Georgia.