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.
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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, Mr Navalny’s team said. Earlier she posted a picture of herself on the way to the rally.
Police say the protests are illegal and Russian authorities have warned that the demonstrations 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”.
In Yakutsk, where temperatures fell to -40C, a protester named Ivan said it was the first rally he had attended.
“I am tired of the despotism and lawlessness of the authorities. No questions have been answered. I want clarity, openness, and change. This is what made me come here,” he said.
Further rallies saw about 1,000 people demonstrate in Omsk, also in Siberia, and about 7,000 people protest in Yekaterinburg in the Ural region, according to local media reports.
The OVD-Info monitoring group said police had detained more than 4,000 people at protests in 85 cities across the country. They included 1,167 held in Moscow and 862 in St Petersburg.
Later on Sunday, Mr Navalny’s Moscow campaign headquarters announced the end of the day’s protests and called on supporters to attend a rally on Tuesday at a Moscow court where a ruling will be made on Mr Navalny’s detention.
A number of close associates of Mr Navalny have been detained since last week and others, including his brother and Pussy Riot activist Maria Alyokhina, have been put under house arrest.
The chief editor of a Russian website specialising in human rights, Sergei Smirnov, was also arrested outside his home on Saturday. News of his detention, apparently over allegations he participated in last week’s protests, has been condemned by other journalists.
In Moscow, police have reportedly been struggling to find space in jail for supporters of the opposition leader.