Mr Udaltsov is charged with organising "mass disorder" during a protest in Moscow in May 2012.

BBC: Russia activist Sergei Udaltsov under house arrest

Mr Udaltsov said the footage was a sham and the documentary "dirt and lies".

BBC: Russia activist Sergei Udaltsov under house arrest

If convicted, Mr Udaltsov and the others face prison sentences of between four and 10 years.

BBC: Travel ban for Russian anti-Putin activist Udaltsov

Last week the SK confined Mr Udaltsov to Moscow after questioning him about the same alleged plot.

BBC: US concern over Russian activist's detention in Kiev

If convicted, Mr Udaltsov faces between four and 10 years in prison.

BBC: Russia activist Sergei Udaltsov under house arrest

One of the best-known figures in the anti-Putin protest movement, Sergei Udaltsov, has been placed under a travel ban by investigators in Moscow.

BBC: Travel ban for Russian anti-Putin activist Udaltsov

On Saturday, investigators asked that Mr Udaltsov be placed under house arrest by the court in Moscow's Basmanny district because he had not been exhibiting good behaviour and had not co-operated with them.

BBC: Russia activist Sergei Udaltsov under house arrest

Two other activists - Konstantin Lebedev, an aide to Mr Udaltsov, and Leonid Razvozzhayev, an aide to opposition MP Ilya Ponomarev - were charged alongside Mr Udaltsov in October but were remanded in custody.

BBC: Russia activist Sergei Udaltsov under house arrest

In a statement released on Wednesday, the SK said it had begun an investigation into Mr Udaltsov, Leonid Razvozzhayev, Konstantin Lebedev and others on the basis of the allegations made in the documentary, Anatomy Of A Protest II.

BBC: Travel ban for Russian anti-Putin activist Udaltsov