Russian opposition leader Alexei Navalny was brought to a Moscow court on Monday after he had been detained at an anti-corruption rally a day earlier.
Thousands took to the streets on Sunday in various cities and towns across Russia to participate in anti-government protests following calls by Navalny and his anti-corruption fond.
In many places including Moscow the authorities called the gathering an illegal provocation.
At least 500 people had been detained only in Moscow, among them Navalny, who was on his way to join protesters rallying along the city's Tverskaya street.
The 40-year old Navalny, arguably Russia's most popular opposition leader, has been twice convicted on fraud and embezzlement charges that he has dismissed as politically motivated. Navalny is currently serving a suspended sentence, and Sunday's arrest could be used as a pretext to convert it into jail time.
Separately, police arrested 17 associates of Navalny's who were at their office, setting up and monitoring a webcast of the rally.
All of them spent the night at the police station while authorities raided their office, reportedly taking out all equipment. It wasn't immediately clear what charges they may be facing.