MOSCOW — Russian opposition leader Alexei Navalny on Tuesday faces a court hearing that could end with him being sent to prison for years. Meanwhile, tens of thousands of people have taken to the streets across Russia to demand the release of jailed opposition leader Navalny, keeping up nationwide protests that have rattled the Kremlin. The 44-year-old, an anti-corruption investigator who is the most prominent critic of President Vladimir Putin, 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 deny the charge and claim, despite tests by several European labs, that they have no proof he was poisoned. Russia’s penitentiary service alleges that Navalny violated the probation conditions of his suspended sentence from a 2014 money-laundering conviction that he has rejected as politically motivated. Russia rebuffs calls from West to release Kremlin critic Alexei Navalny from detention. It has asked the Simonovsky District Court in Moscow to turn his 3.5-year suspended sentence into one that he must serve in prison. Navalny and his lawyers have argued that while he was recovering in Germany from the poisoning, he could not register with Russian authorities in person as required by the terms of his probation. Navalny also insisted that his due process rights were crudely violated during his arrest and described his jailing as a travesty of justice. Navalny"s jailing has triggered massive protests across Russia over the past two weekends, in which tens of thousands took to the streets to demand his release, chanting slogans against Putin. Police detained over 5,750 people during Sunday"s rallies, including more than 1,900 in Moscow, the biggest number the nation has seen since Soviet times. Most were released after being handed court summons and face fines or jail terms of seven to 15 days. Several people face criminal charges over alleged violence against police. One of those taken into custody for several hours was Navalny’s wife, Yulia, who was ordered Monday to pay a fine of about €219 for participating in an unauthorized rally. The massive protests came despite efforts by Russian authorities 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 had seen in years. Despite threats of jail terms, warnings to social media groups and tight police cordons, the protests again engulfed cities across Russia’s 11 time zones on Sunday. Navalny"s team has called for another demonstration on Tuesday outside the Moscow court building. Police were deployed in force near the court building and cordoned off nearby streets, making random detentions. After his arrest, Navalny’s team released a two-hour YouTube video featuring an opulent Black Sea residence allegedly built for Putin. The video has been viewed over 100 million times, fueling discontent as ordinary Russians struggle with an economic downturn and the coronavirus pandemic. Putin insisted last week that neither he nor his relatives own any of the properties mentioned in the video, and his long time confidant, construction magnate Arkady Rotenberg, claimed that he owned the mansion. As part of efforts to quash the protests, the authorities have targeted Navalny’s associates and activists across the country. His brother Oleg, top ally Lyubov Sobol and several others were put under house arrest for two months and face criminal charges of violating coronavirus restrictions. The jailing of Navalny and the crackdown on protests have stoked international outrage, with Western officials calling for his release and condemning the arrests of demonstrators. Russia has dismissed the comments from foreign officials as interfering in its domestic affairs. — Agencies