Thousands of Russians took part in protests demanding the release of jailed opposition leader Alexei Navalny.
More than 5,000 people have been detained, according to monitoring groups. In Moscow police closed metro stations and blocked off the city centre.
In a massive show of force, police imposed a sweeping security lockdown in the heart of Moscow, sealing off streets to pedestrians near the Kremlin, closing metro stations and deploying hundreds of riot police as snow fell.
At one point, a column of protesters marched towards the prison in northern Moscow where Navalny is being held, chanting “Let him go!”. In another scene, people in a crowd raised their hands above their heads in front of a row of riot police and chanted “we’re not your enemies”.
Police said protesters could face criminal prosecution for attending or calling for an unauthorised demonstration and warned they could spread COVID-19.
Navalny’s allies used social media to repeatedly change the location of their rally, scattering the crowds over different parts of Moscow and making it harder to disperse.
Police put turnout at Sunday’s Moscow protest at around 2,000 people, but several organizations put numbers in thousands.
In St Petersburg and Moscow police used force to detain protesters and were occasionally seen using tasers. One protester had a bloodied, bandaged head.
At least 5,021 people were detained nationwide, including 1,608 in Moscow, according to OVD-Info, a protest monitoring group.
Why are they protesting?
Opposition leader Alexei 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 was arrested after arriving in Moscow from Germany, 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.