Kremlin critic Alexei Navalny was released on Friday after serving 30 days in jail for planning opposition protests, which have grown into a movement that has shaken Moscow since last month.

Russian opposition supporters plan a major protest in Moscow on Saturday after police detained thousands at recent demonstrations that have been among the largest since President Vladimir Putin's return to the Kremlin in 2012.

Russia on Thursday froze the assets of an anti-corruption group that top opposition figure Alexei Navalny set up to expose the questionable wealth of top government officials, his spokeswoman said.

Russian opposition leader Alexei Navalny was "poisoned" by an unidentified toxic substance but doctors have sent him back to jail despite his condition, his lawyer and personal physician said Monday.

Russia's jailed opposition politician Alexei Navalny might have been exposed to an unidentified "toxic agent," his personal doctor said on Monday, while health officials insisted his condition was satisfactory.

Russian opposition leader Alexei Navalny said he was arrested on Wednesday, in an apparent move by the authorities to prevent a major protest rally this week.

More than 20,000 people packed a Moscow square Saturday to protest the authorities' refusal to allow opposition candidates to register for local polls.

Russian opposition leader Alexei Navalny said Tuesday he was prevented from flying out of a Moscow airport to travel to France and attend the European Court of Human Rights.

Russian opposition leader Alexei Navalny was detained Monday on his release from prison after serving a 30-day sentence for an unauthorised protest.

Russia on Tuesday said it has officially warned US internet giant Google against meddling in next Sunday's local elections by posting opposition leader Alexei Navalny's videos calling for mass protests.

A Moscow court on Monday gave a 30-day jail sentence to Russian opposition leader Alexei Navalny over an unsanctioned protest earlier this year, just days before another planned political rally.

Russian opposition politician Alexei Navalny called Tuesday for nationwide protests to take place across the country during the World Cup over a government plan to raise the retirement age for the first time in its modern history.