Thousands of Russians have been taking part in unauthorised protests to demand the release of the jailed opposition leader Alexei Navalny.

More than 4,000 people have been detained, a monitoring group says. In Moscow police closed metro stations and blocked off the city centre.

Mr Navalny was jailed on his return to Russia after recovering from an attempt to kill him with a nerve agent.

He blames the security services for the attack but the Kremlin denies this.

The opposition figure had only just arrived from Berlin, where he spent months recovering from the near-fatal incident.

Russian authorities say Mr Navalny 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 had allowed him to travel to Berlin for treatment for the Novichok poisoning, which happened in Russia last August.

Mr Navalny has blamed state security agents under Mr Putin's orders for the attempt on his life and investigative journalists have named Russian FSB agents suspected of the poisoning. But the Kremlin denies involvement and disputes the conclusion, by Western weapons experts, that Novichok was used.

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.

Protesters then attempted to reach the Matrosskaya Tishina prison where Mr Navalny is being held.

Mr Navalny's wife, Yulia Navalnaya, was among those detained at Sunday's protest. She was later released.

Ahead of the protests she posted on Instagram: "If we stay quiet, then they could come for any of us tomorrow."

Police said the protests were illegal and Russian authorities warned that the gatherings could spread the coronavirus.

A 40-year-old protester in Moscow told Reuters: "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 also took 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".

•Text (excluding headline): BBC.

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