Around 150 people have been arrested in Moscow during a forum of independent members of municipal councils.
Police showed up at the gathering shortly after it opened, saying that all those present would be detained
They are accused of taking part in an event arranged by an "undesirable organisation", according to OVD-Info, an independent group monitoring political repression.
It follows the Russian authorities clamping down on anti-Kremlin opinions after opposition leader Alexei Navalny was arrested when he returned from Berlin in January.
Security forces escorted the arrested people to buses, which took them to police stations where they were charged with "administrative violations".
The detained included leading opposition figures, like Yulia Galyamina.
"My right to be wherever I want is being violated. I didn't break any law, I'm a municipal deputy, a government representative," she told officers.