Moscow is braced for more protests seeking the release of Alexei Navalny who faces a court hearing on 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 on Sunday, chanting slogans against President Vladimir Putin and demanding freedom for Mr Navalny, the opposition leader who was jailed last month and faces years in prison.

More than 5,400 protesters were detained by authorities, according to a human rights group.

One of those taken into custody for several hours was Mr Navalny’s wife Yulia, who was ordered to pay a fine of about £190 for participating in an unauthorised rally.

While state-run media dismissed the demonstrations as small and claimed they showed the failure of the opposition, Mr Navalny’s team said the turnout demonstrated “overwhelming nationwide support” for the Kremlin’s fiercest critic.

His allies called for protesters to go to the Moscow courthouse on Tuesday, adding: “Without your help, we won’t be able to resist the lawlessness of the authorities.”

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 Mr Navalny.

He was arrested on January 17 on 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 three and a half-year suspended sentence with a custodial term. The prosecutor general’s office backed the motion on Monday, alleging Mr Navalny engaged in “unlawful conduct” during the probation period.

After his arrest, Mr Navalny’s team released a two-hour YouTube video alleging that an opulent Black Sea residence was built for Mr Putin. The video has been viewed more than 100 million times, further stoking Russians’ discontent amid an economic downturn.

The Kremlin says Mr Putin is not connected to the residence, and the president addressed the allegations last week, saying neither he nor his relatives own any of the properties mentioned in the video.

The rallies following Mr Navalny’s arrest appear to have rattled the Kremlin. To try to quell the protests, authorities have jailed his 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, Mr Navalny’s spokeswoman Kira Yarmysh was put under house for two months in connection with the same charge. She was ordered to serve nine days in jail last month for violating protest regulations and was supposed to be released on 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 organisation Agora.

Police cracked down hard on the demonstrators on Sunday, detaining more than 5,400, 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.

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 behaviour toward law enforcement officers”.