Over 200 people were detained on Monday by police at opposition protests called by Kremlin critic Alexei Navalny, said a Russian NGO tracking arrests.
"About 121 people were detained in Moscow up to this point. In Saint-Petersburg - 137," OVD-Info group, which operates a detention hotline, wrote on Twitter.
AFP correspondents in central Moscow observed riot police lining up the main Tverskaya Street thoroughfare where Navalny's supporters were chanting "Shame!" and waving Russian tricolour flags.
Others were shouting "Freedom to Navalny" after the politician himself was picked up by police on his way to the protest in the stairwell of his building.
A correspondent in Saint Petersburg estimated about two hundred people detained in the centre, where demonstrators flocked to protest after authorities allowed them to gather only in a far-off spot in the north of the city.
Local media in Russia's southern resort Sochi said 25 people were detained after attempting to rally, and OVD-Info added that about 10 arrests occurred in each Vladivostok and northern city of Norilsk.