TALLINN, Estonia (AP) — Russian prosecutors asked a court to sentence imprisoned opposition leader Alexei Navalny to 20 years in prison on extremism charges, his ally Ivan Zhdanov said Thursday.

According to Zhdanov, the trial against Navalny, which went on behind closed doors in the prison where the politician is serving another lengthy sentence, is scheduled to conclude with a verdict on Aug. 4.

Navalny, 47, is President Vladimir Putin's fiercest foe who exposed official corruption and organized major anti-Kremlin protests. He was arrested in January 2021 upon returning to Moscow after recuperating in Germany from nerve agent poisoning that he blamed on the Kremlin.

The authorities sentenced him to 2 1/2 years in prison for parole violations and then to another nine years on charges of fraud and contempt of court. The politician is currently serving his sentence in a maximum-security prison east of Moscow.

The new charges relate to the activities of Navalny’s anti-corruption foundation and statements by his top associates. His allies said the charges retroactively criminalize all the foundation's activities since its creation in 2011.

Navalny has rejected all the charges against him as politically motivated and accused the Kremlin of seeking to keep him behind bars for life.