Thousands of Russians have been taking part in unauthorised protests to demand the release of the jailed opposition leader Alexei Navalny.
More than 1,000 people have been detained so far, local media say.
In Moscow police have closed metro stations and are restricting movement in the city centre. About 140 people have been detained there.
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.
The opposition figure had only just arrived from Berlin, where he spent months recovering from the near-fatal attack.
Russian authorities say he was supposed to report to police regularly because of a suspended sentence for embezzlement.
Mr Navalny has denounced his detention as “blatantly illegal”, saying the authorities knew he was being treated in Berlin for the Novichok poisoning, which happened in Russia last August.
Meanwhile Russian President Vladimir Putin has denied reports he is the owner of a vast palace on the Black Sea, as alleged by Mr Navalny in a video that has gone viral in Russia and has been watched more than 100m times.
In Moscow the BBC’s Sarah Rainsford says protesters played cat-and-mouse with police, getting up close to officers before retreating to safety. Police snatch squads pulled some protesters through the lines of riot shields. Footage showed a stream of people being escorted on to buses by riot police.
Mr Navalny’s wife Yulia Navalnaya is among those detained, Mr Navalny’s team says.
Police say the protests are illegal, while Russian authorities have warned that the demonstrations could spread the coronavirus.
A 40-year-old protester in Moscow told Reuters she had attended despite having a panic attack the night before over the possible repercussions she could face for taking part.
“I understand that I live in a totally lawless state. In a police state, with no independent courts. In a country ruled by corruption. I would like to live differently,” she said.
In St Petersburg, Mr Putin’s home city, a crowd gathered in a central square and chanted: “Down with the Tsar.”
Rallies in support of Mr Navalny have already taken place in eastern Russia. In the Siberian city of Novosibirsk, at least 2,000 people marched through the city chanting “Freedom” and “Putin is a thief”.
