Chanting slogans against President Vladimir Putin, thousands of people took to the streets Sunday across Russia’s vast expanse to demand the release of jailed opposition leader Alexei Navalny, keeping up the nationwide protests that have rattled the Kremlin. Over 5,100 were detained by police, according to a 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 tight police cordons, the protests again engulfed many cities on Sunday.

The 44-year-old Navalny, an anti-corruption investigator who is Putin’s best-known critic, was arrested on Jan. 17 upon returning 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 when he was recuperating in Germany.

The United States urged Russia to release Navalny and criticized the crackdown on protests.

“The U.S. condemns the persistent use of harsh tactics against peaceful protesters and journalists by Russian authorities for a second week straight,” U.S. Secretary of State Antony Blinken said on Twitter.

On Sunday, police detained more than 2,700 people at protests held in cities across Russia’s 11 time zones, according to OVD-Info, a group that monitors political arrests.

In Moscow, authorities introduced unprecedented security measures in the city center, closing subway stations near the Kremlin, cutting bus traffic and ordering restaurants and stores to stay closed.

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 Navalny claims was responsible for his poisoning. Facing police cordons around the square, the protest shifted to other central squares and streets.

Police were randomly picking up people and putting them into police buses, but thousands of protesters marched across the city center, 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 Navalny’s team.

At some point, crowds of demonstrators walked toward the Matrosskaya Tishina prison where Navalny is being held, but met phalanxes of riot police who pushed the march back and chased protesters through courtyards, detaining scores. Still, protesters marched around the Russian capital for hours, zigzagging around police cordons.

Nearly 700 people were detained in Moscow, including 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.

An estimated 2,000 marched across Russia’s second-largest city of St. Petersburg, and occasional scuffles erupted as some demonstrators pushed back police who tried to make detentions. Nearly 400 were arrested.

In the far eastern port of Vladivostok, at least 120 people were detained after protesters danced on the ice and rallied in the city center.

As part of a multipronged effort by authorities to block the protests, courts have jailed 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 Friday under a two-month house arrest 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 Jan. 23 calling for Navalny’s release 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.

Just after Navalny’s arrest, his team released a two-hour video on his YouTube channel about the Black Sea residence purportedly built for 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 Putin’s time in office while poverty has remained widespread.

Demonstrators in Moscow chanted “Aqua discotheque!,” a reference to one of the fancy amenities at the residence that also features a casino and a hookah lounge equipped for watching pole dances.

Putin says that neither he nor any of his close relatives own the property. On Saturday, construction magnate Arkady Rotenberg, a longtime Putin confidant and his occasional judo sparring partner, claimed that he himself owned the property.

Navalny fell into a coma on Aug. 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 Organization for the Prohibition of Chemical Weapons, established that he was exposed to the Novichok nerve agent. Russian authorities have refused to open a full-fledged criminal inquiry, claiming a lack of evidence that he was poisoned.

Navalny was arrested immediately when he returned to Russia earlier this month and jailed for 30 days on the request of Russia’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 Navalny’s appeal to be released, and another hearing next week could turn his 3 1/2-year suspended sentence into one he must serve in prison.

(AP)