Hundreds of people have been detained as police try to stop nationwide protests in Russia in support of jailed opposition politician Alexei Navalny.
Mr Navalny’s wife, Yulia, said she had been detained at a protest in Moscow, where tens of thousands have gathered.
They were met by large numbers of riot police in the capital’s Pushkin Square, and beaten back with batons.
Mr Navalny, President Vladimir Putin’s most high-profile critic, called for protests after his arrest last weekend.
He was detained on 17 January after he flew back to Moscow from Berlin, where he had been recovering from a near-fatal nerve agent attack in Russia last August.
On his return, he was immediately taken into custody and found guilty of violating parole conditions. He says it is a trumped-up case designed to silence him, and has called on his supporters to protest.
Prior to the rallies, Russian authorities had promised a tough crackdown, with police saying any unauthorised demonstrations and provocations would be “immediately suppressed”. Several of Mr Navalny’s close aides, including his spokeswoman Kira Yarmysh, were arrested.
OVD Info, an independent NGO that monitors rallies, said that more than 1,600 people had been detained during protests across the country on Saturday.
Teenagers were among the many Navalny supporters who joined the demonstration in Moscow’s central Pushkin Square. They were later forced by police to disperse to neighbouring streets.
Russia’s interior ministry said 4,000 had turned up in Moscow, but opposition sources and reporters on the ground say it was in the tens of thousands.
According to OVD Info, more than 500 people were detained in Moscow alone.
Among them was Lyubov Sobol, a prominent aide of Mr Navalny who had already been fined for urging Russians to join the protests. She tweeted a video of police roughly pulling her away from an interview with reporters.
Mr Navalny’s wife, Yulia, also said she was being held by police at the same protest, posting an image on her Instagram account with the caption: “Apologies for the poor quality. Very bad light in the police van.”
Prominent Navalny activists are also being held in the cities of Vladivostok, Novosibirsk and Krasnodar.
At the scene – by Steve Rosenberg, Moscow correspondent
Moscow’s Pushkin square is packed with anti-government protesters. “Freedom to Navalny” they’re chanting, “Putin go away!”
There are long lines of riot police around the square and down Moscow’s main street, Tverskaya, less than a mile from the Kremlin.
“This is an illegal gathering” the police are announcing through loudspeakers, “please leave.”
There’s a cacophony of car horns sounded by drivers passing the square, a show of support for the protesters.
One driver had hung a pair of underpants out of his car window, a reference to Mr Navalny’s poisoning. The Novichok nerve agent had allegedly been applied to Alexei Navalny’s underwear.
One woman in the crowd told me she decided to take part in the protest because “Russia has been turned into a prison camp,” and to support the country’s most prominent opposition figure, who is behind bars.
Russia’s Far East saw some of the first protests on Saturday, with people braving the extreme cold in a show of support for Mr Navalny.
Attendees at a small protest in the Siberian city of Yakutsk saw temperatures dip as low as -50C (-58F).
One independent news source, Sota, said at least 3,000 people had joined a demonstration in the city of Vladivostok but local authorities there put the figure at 500.
AFP footage showed riot police in Vladivostok running into a crowd, and beating some of the protesters with batons.
Meanwhile, there were reports of disruption to mobile phone and internet coverage in Russia on Saturday – though it is not known if this is related to the protests.
The social media app TikTok had been flooded with videos promoting the demonstrations and sharing viral messages about Mr Navalny.
In response, Russia’s official media watchdog, Roskomnadzor, demanded that TikTok take down any information “encouraging minors to act illegally”, threatening large fines.
Russia’s education ministry has also told parents not to allow their children to attend any demonstrations.
In a push to gain support ahead of the protests, Mr Navalny’s team released a video about a luxury Black Sea resort that they allege belongs to President Putin – an accusation denied by the Kremlin.