More than 130 people have been arrested as supporters of opposition leader Alexei Navalny hold protests in some 80 cities across Russia, reports say, according to BBC.
They are demanding he be allowed to stand in 2018 presidential elections.
Clashes and arrests have been reported in St Petersburg, where the main protest is 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.
Media reports say there were mass arrests at the protest, attended by as many as 3,000 people, when a group of demonstrators tried to break through a police line.
A Reuters witness saw at least 10 people detained.
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, according to human rights website OVD-Info.
Meanwhile several people were arrested as hundreds rallied in Moscow’s Pushkin Square, though all were reportedly later released.
The largest number of arrests was 20 in the city of Lipetsk, south-east of Moscow, OVD-Info said.
Protesters shouted “Russia will be free” and “Free Navalny”. Others called for Mr Putin not to stand in the election.