More than 250 people have been arrested as supporters of opposition leader Alexei Navalny hold protests in some 80 cities across Russia, reports say.
They are demanding he be allowed to stand in 2018 presidential elections.
Clashes and dozens of arrests have been reported in St Petersburg, where the main protest has been taking place.
The rallies coincide with President Vladimir Putin's 65th birthday. Most are unauthorised, including those in Moscow and St Petersburg.
Mr Navalny is currently serving 20 days in jail for repeatedly violating a law on organising public meetings.
It is the third time this year that Mr Navalny has been jailed.
Russia's electoral authorities say he cannot stand in the March vote because of a separate suspended sentence.
In recent months he has travelled across Russia in a bid to bolster his makeshift election campaign.
Mr Navalny had been due to attend the main rally taking place on Saturday evening in St Petersburg, Mr Putin's home city.
As many as 3,000 people were at the demonstration in Russia's second city, many of them carrying "Navalny 2018" banners.
Media reports say there were a large number of arrests after a group of demonstrators tried to break through a police line.
According to the human rights website OVD-Info, 62 people were detained. Most were later released.
Several other organisers of the rally and leaders of the pro-democracy group Open Russia - sponsored by exiled former oil tycoon Mikhail Khodorkovsky - were arrested in the city earlier on Saturday, the website said.
Earlier several people were arrested as hundreds rallied in Moscow's Pushkin Square, though all were reportedly later released.
Police urged people to disperse but did not move to break up the rally. Some protesters marched towards the Kremlin, but were blocked by police.
Elsewhere demonstrations ranged from a few dozen people to more than 100 in the Siberian city of Novosibirsk.
Protest organisers were pre-emptively detained in Smolensk, Tver, Stavropol, Irkutsk, Yakutsk and Perm, media reports say.
OVD-Info put the total number of arrests at 271 in 26 cities, with 57 in Yaroslavl, 21 in Krasnodar and 20 in Lipetsk.