Riot police arrested four opposition leaders at an anti-Putin rally in Moscow on Saturday.
The rally, techinically illegal, took place at the former KGB security police's headquarters, and were intended to mark one year from the first anti-Putin demonstrations.
Protesters marched shouting, "Free political prisoners!", and "Down with the police state".
Alexei Navalny, Sergei Udaltsov, IIya Yashin and Ksenia Sobchak were detained.
Navalny, an anti-corruption blogger, shouted as he was being taken away, "the bloody regime has got to Sobchak".