More than 500 people have been detained as rallies in support of jailed opposition leader Alexei Navalny begin across Russia, a monitoring group says.
In Moscow police have closed metro stations and are restricting movement in the city centre. About 100 people have been detained there, Reuters says.
Mr Navalny was jailed on his return to Russia after recovering from an attempt to kill him with a nerve agent.
He is accused of not complying with a suspended sentence.