Thousands of anti-government activists challenging President Vladimir Putin's rule are protesting across Russia with police arresting main opposition leader Alexei Navalny outside his Moscow home.
Navalny's wife, Yulia, said on Twitter that he was arrested about a half-hour before the Moscow demonstration was to begin. Police later confirmed the arrest, saying he could get up to 15 days in jail on charges of failing to follow police orders and violating public order.
Although city authorities had agreed to a location for the Moscow protest, Navalny called for it to be moved to Tverskaya Street, one of Moscow's main thoroughfares.
He said contractors hired to build a stage at the agreed-upon venue could not do their work after apparently coming under official pressure.
Tverskaya, known in Soviet times as Gorky Street, was closed off to traffic on Monday for an extensive commemoration of the national holiday Russia Day, including people dressed in historical Russian costumes.
Moscow police blocked part of the street with big dump trucks in a bid to block the movement of protesters.
Associated Press journalists witnessed at least 50 arrests in the St Petersburg with Russian media reporting at least 150 arrested. AP reporters also saw at least 10 arrests in Moscow, with reports saying there were up to 100 so far in the capital.
The protesters, some carrying Russian flags, were chanting loudly as Moscow riot police stood watch.
A regional security official, Vladimir Chernikov, told Ekho Moskvy radio that police wouldn't interfere with demonstrators on the street - as long as they didn't carry placards or shout slogans.
The Kremlin has long sought to cast the opposition as a phenomenon of a privileged, Westernised urban elite out of touch with people in Russia's far-flung regions. But Monday's protests could demonstrate that it has significant support throughout the vast country.
Navalny's website reported that protests were held in more than a half-dozen cities in the far east, including the major ports of Vladivostok and Khabarovsk and in Siberia's Barnaul.
Eleven demonstrators were arrested in Vladivostok, according to OVD-Info, a website that monitors political repressions.
Navalny has become the most prominent figure in an opposition that has been troubled by factional disputes. He focuses on corruption issues and has attracted a wide following through savvy use of internet video.
Navalny has announced his candidacy for the presidential election in 2018.