MOSCOW (AP) — Moscow braced for more protests seeking the release of jailed opposition leader Alexei Navalny, who faces a court hearing Tuesday after two weekends of nationwide rallies and thousands of arrests in the largest outpouring of discontent in Russia in years.

Tens of thousands filled the streets across the vast country Sunday, chanting slogans against President Vladimir Putin and demanding freedom for Navalny, who was jailed last month and faces years in prison. Over 5,400 protesters were detained by authorities, according to a human rights group.

One of those taken into custody for several hours was Navalny's wife, Yulia, who was ordered Monday to pay a fine of about $265 for participating in an unauthorized rally.

While state-run media dismissed the demonstrations as small and claimed that they showed the failure of the opposition, Navalny’s team said the turnout demonstrated “overwhelming nationwide support” for the Kremlin's fiercest critic. His allies called for protesters to come to the Moscow courthouse on Tuesday.

“Without your help, we won't be able to resist the lawlessness of the authorities,” his politician's team said in a social media post.

Mass protests engulfed dozens of Russian cities for the second weekend in a row despite efforts by authorities to stifle the unrest triggered by the jailing of 44-year-old Navalny.

He was arrested Jan. 17 upon returning from Germany, where he spent five months recovering from nerve-agent poisoning that he blames on the Kremlin. Russian authorities reject the accusation. He faces a prison term for alleged probation violations from a 2014 money-laundering conviction that is widely seen as politically motivated.

Last month, Russia's prison service filed a motion to replace his 3 1/2-year suspended sentence from the conviction with one he must serve. The Prosecutor General's office backed the motion Monday, alleging Navalny engaged in “unlawful conduct” during the probation period.

After his arrest, Navalny's team released a two-hour YouTube video alleging that an opulent Black Sea residence was built for Putin. The video has been viewed over 100 million times, further stoking Russians' discontent amid an economic downturn. The Kremlin says Putin is not connected to the residence, and the president addressed the allegations himself last week, saying neither he nor his relatives own any of the properties mentioned in the video.

The rallies following Navalny's arrest appear to have rattled the Kremlin. To try to quell the protests, the authorities have jailed Navalny’s associates and activists across the country. His brother Oleg, top ally Lyubov Sobol and three others were put under house arrest for two months and face criminal charges of violating coronavirus restrictions.

On Tuesday, Navalny's spokeswoman Kira Yarmysh was also put under house for two months in connection with the same charge. Yarmysh was ordered to serve nine days in jail last month for violating protest regulations and was supposed to be released Saturday, but was arrested again.

At least 40 criminal investigations have been opened in 18 Russian regions in connection with the protests, said Pavel Chikov, head of the human rights organization Agora.

Police cracked down hard on the demonstrators Sunday, detaining over 5,400 of them, according to OVD-Info, a legal aid group that monitors arrests at protests. The group said that was the biggest number in its nine-year history of keeping records in the Putin era.

At least 51 protesters were beaten by police while being detained, OVD-Info said. Videos of the protests showed riot police striking people with truncheons and throwing them to the ground. Media reported some police used stun guns on protesters.

When asked about the mass detentions, Kremlin spokesman Dmitry Peskov said the protests were “unlawful” and charged that “there was a fairly large number of hooligans, provocateurs with more or less aggressive behavior toward law enforcement officers."

“In response to provocations, the police act harshly and within the law,” Peskov said.

State media also highlighted “aggressive actions” by protesters in their coverage, which said the rallies Sunday drew far fewer people than the previous one on Jan. 23. Many reports underscored “polite” actions by police officers, and state TV channel Russia 1 even showed video statements of people thanking law enforcement officers in connection with the rallies.

The jailing of Navalny and the crackdown on protests prompted international outrage, with Western officials calling for his release and condemning the arrests of demonstrators.

The German government urged the immediate release of the arrested protesters, as well as Navalny. It “condemns the use of force by Russian security forces and the once again disproportionate action against peacefully demonstrating citizens,” government spokeswoman Martina Fietz said.

U.S. Secretary of State Antony Blinken tweeted that Washington "condemns the persistent use of harsh tactics against peaceful protesters and journalists by Russian authorities for a second week straight.” He also urged the release of Navalny and those detained “for exercising their human rights.”

The Russian Foreign Ministry rejected Blinken’s call as “crude interference in Russia’s internal affairs” and accused Washington of trying to destabilize the situation by backing the protests.