MOSCOW, FEBRUARY 02

Russian opposition leader Alexei Navalny faced a court hearing Tuesday that could end with him being sent to prison for years.

The 44-year-old Navalny, an anti-corruption investigator who is the most prominent critic of President Vladimir Putin, was arrested Jan. 17 upon returning from Germany, where he spent five months recovering from a nerve-agent poisoning that he blames on the Kremlin. The accusation has been rejected by the Russian authorities.

Russia's penitentiary service alleged that Navalny had violated the probation of his suspended sentence from a 2014 money-laundering conviction that he has rejected as politically motivated. It asked the Simonovsky District Court in Moscow to turn his 3 1/2-year suspended sentence into one that he must serve in prison.

Navalny and his lawyers have argued that while he 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. Many protesters also chanted slogans against Putin. Police detained thousands of participants each time. Some were beaten.

Navalny's team has called for another demonstration outside the Moscow court building on Tuesday. Police have deployed in force near the court building and cordoned off nearby streets.