Thousands of people took to the streets across Russia on Sunday to demand the release of jailed opposition leader Alexei Navalny, keeping up the nationwide protests that have rattled the Kremlin.
More than 3,000 people were detained by police, according to one monitoring group.
Russian authorities mounted a massive effort to stem the tide of demonstrations after tens of thousands rallied across the country last weekend in the largest, most widespread show of discontent that Russia has seen in years.
Yet despite threats of jail terms, warnings to social media groups and notable displays of riot police, the protests again engulfed many cities on Sunday.
Mr Navalny, 44, an anti-corruption investigator who is President Vladimir Putin's best-known critic, was arrested on January 17 on his return from Germany, where he spent five months recovering from a nerve-agent poisoning that he blames on the Kremlin.
Russian authorities have rejected the accusations.
He was arrested for allegedly violating his parole conditions by not reporting for meetings with law enforcement while recuperating in Germany.
The United States urged Russia to release Mr Navalny and criticised the crackdown on protests.
"The US condemns the persistent use of harsh tactics against peaceful protesters and journalists by Russian authorities for a second week straight," US Secretary of State Antony Blinken said on Twitter.
Police detained nearly 2,300 people at protests held in cities across Russia's 11 time zones on Sunday, according to OVD-Info, a group that monitors political arrests.
In Moscow, authorities introduced unprecedented security measures in the city centre, closing underground stations near the Kremlin, cutting bus traffic and ordering restaurants and shops to stay closed.
Mr Navalny's team initially called for Sunday's protest to be held on Moscow's Lubyanka Square, home to the main headquarters of the Federal Security Service, which Mr Navalny claims was responsible for his poisoning.
After police cordoned off the area around the square, the protest shifted to another central square a mile away. Officers deployed in force at this location too, randomly picking up people and putting them in police buses.
But hundreds of others marched across the city centre, chanting "Putin, resign!" and "Putin, thief!", a reference to an opulent Black Sea estate reportedly built for the Russian leader that was featured in a widely popular video released by Mr Navalny's team.
Some later marched to the Matrosskaya Tishina prison where Mr Navalny is being held, but met phalanxes of riot police who chased them back and detained scores.
More than 500 people were detained in Moscow, including Mr Navalny's wife, Yulia, who joined the protest.
The city of Novosibirsk in eastern Siberia saw one of the biggest rallies, with several thousand people marching across the city. Over 100 protesters were detained at this demonstration.
An estimated 2,000 marched across Russia's second-largest city, St Petersburg, and occasional scuffles erupted as some demonstrators pushed back police who tried to make detentions.
In the far eastern port of Vladivostok, at least 120 people were detained after protesters danced on the ice and rallied in the city centre.
Meanwhile, as part of a multipronged effort by authorities to block the protests, courts have jailed Mr Navalny's associates and activists across the country over the past week.
His brother Oleg, top aide Lyubov Sobol and three other people were put under two-month house arrest on Friday on charges of allegedly violating coronavirus restrictions during last weekend's protests.
Prosecutors also demanded that social media platforms block calls to join the protests.
The Interior Ministry has issued stern warnings to the public not to join the protests, saying participants could be charged with taking part in mass riots, which carries a prison sentence of up to eight years. Those engaging in violence against police could face up to 15 years.
Nearly 4,000 people were reportedly detained at demonstrations on January 23 calling for Mr Navalny's release which took place in more than 100 Russian cities, and some were given fines and jail terms. About 20 were accused of assaulting police and faced criminal charges.
Shortly after Mr Navalny's arrest, his team released a two-hour video on his YouTube channel about the Black Sea residence purportedly built for Mr Putin. The video has been viewed over 100 million times, helping fuel discontent and inspiring a stream of sarcastic jokes on the internet amid an economic downturn.
Russia has seen extensive corruption during Mr Putin's time in office even as many ordinary citizens struggle financially.
Mr Putin says that neither he nor any of his close relatives own the property.
Mr Navalny fell into a coma on August 20 while on a domestic flight from Siberia to Moscow. He was transferred to a Berlin hospital two days later. Labs in Germany, France and Sweden, and tests by the Organisation for the Prohibition of Chemical Weapons, established that he was exposed to the Novichok nerve agent. Russian authorities have refused to open a fully-fledged criminal inquiry, claiming a lack of evidence that he was poisoned.
Mr Navalny was arrested immediately on his return to Russia on January 17 and jailed for 30 days on the request of the country's prison service, which alleged he had violated the probation of his suspended sentence from a 2014 money-laundering conviction that he has rejected as political revenge.
On Thursday, a Moscow court rejected Mr Navalny's appeal to be released, and another hearing next week could turn his three-and-a-half-year suspended sentence into one he must serve in prison.