A Russian court has placed opposition leader Sergei Udaltsov under house arrest for two months, the Interfax news agency reported Saturday.
Udaltsov, 35, is not allowed to leave his Moscow home without permission from the authorities until April 6, and also cannot maintain contact with relatives or lawyers.
He is also banned from using the internet and telephone.
The court said that he had violated regulations and was also a flight risk.
Udaltsov was formally charged in October with conspiracy to organize violent protests. If convicted, he could face up to 10 years in prison.
The opposition said the arrest was politically motivated. Udaltsov said the move was part of a campaign against the liberal opposition in Russia.
A pro-Kremlin television channel reported in October that Udaltsov and opposition groups planned the violent takeover of several Russian cities.
The broadcaster aired what it claimed were secret recordings of Udaltsov reportedly discussing his plans for a power grab with Georgian parliamentarians.
Udaltsov, the head of the opposition group Left Front, dismissed the report as "propaganda."
He has been arrested several times on minor charges and has organized street protests against President Vladimir Putin, with tens of thousands of participants.
He is accused of using foreign funds to fuel demonstrations in May.