Russia police have raided the Moscow office of opposition leader Alexei Navalny as demonstrations calling for a boycott of Russia's presidential election take place across the country.
A video stream Sunday morning from Navalny's headquarters showed police entering the office. One broadcaster on the stream said police apparently were using a grinder to try to get access to the broadcast studio.
The anchors said police said they had come because of a bomb threat.
One anchor, Dmitri Nizovtsev, was detained by police during the raid, according to video broadcast by the gheadquarters. Navalny's Moscow co-ordinator, Nikolai Lyaskin, also was detained on Sunday, the Interfax news agency quoted him as saying.
Navalny, who has been blocked from running in Russia's March 18 presidential election, called for nationwide protests on Sunday.
Sizeable gatherings have been reported Sunday in the Far East and Siberia, including one in remote Yakutsk where the temperature reportedly was minus-45 C (minus-49 F). More are set for Moscow and St. Petersburg in the afternoon.
Several hundred demonstrators assembled on the centre square of the Pacific port city of Vladivostok, complaining both of President Vladimir Putin, who is running for a fourth term, and of the exclusion of Navalny.
Navalny was prevented from running because of his conviction on an embezzlement charge in a case widely seen as politically motivated.
"They took these elections away from us, they took away our votes. Our candidate was not allowed to run," said Vladivostok demonstrator Dmitri Kutyaev.
Navalny rose to prominence with detailed reports about corruption among top Russian officials, which he popularized on social media to circumvent state control of television.
Last year, he called for two demonstrations which attracted people throughout the country, undermining critics' claims that he appeals only to a narrow segment of prosperous urbanites.