Police detained more than 1,000 people including dozens in Moscow during demonstrations across Russia on Sunday calling for the release of jailed Kremlin critic Alexei Navalny, a monitor said.
The OVD-Info monitor said 1,009 people had been detained, including 142 in Moscow where protesters were gathering in various locations after police locked down access to the city centre.
Navalny was detained at a Moscow airport in mid-January after flying back to Russia from Germany where he was recovering from an August poisoning he blames on the Kremlin.
The 44-year-old anti-corruption campaigner is being held in a Moscow detention centre and facing years of potential jail time in several different criminal cases, despite calls from Western governments for his release.
In moves not seen in years in Moscow, police locked down the centre of the capital on Sunday, with hundreds lining the streets, central Metro stations closed and the movements of pedestrians restricted.
Protesters who had hoped to gather outside the headquarters of the FSB security service were instead scattered to various parts of the city as organisers made last-minute changes in locations.
AFP journalists saw dozens of protesters detained and forced into police vans. It was unclear amid the chaos how many people were taking part