A Moscow court on Saturday convicted top Kremlin critic Alexei Navalny of defamation, just hours after another court upheld an order for him to serve more than two years in prison in another case.

Judge Vera Akimova said Navalny was guilty of defaming a World War II veteran who was among a group of Russians Navalny called "traitors" for appearing in a pro-Kremlin video.

The verdict was still being read and a sentence not yet imposed, an AFP journalist in the courtroom said.

Prosecutors have asked for Navalny to be fined the equivalent of $13,000.

Before the judge began reading the verdict Navalny made jokes and spoke to reporters from inside his glass box.

"Why are you so sad?" he said, adding he was trying to make ice cream in jail and had already made pickled cucumbers.

Earlier Saturday another court upheld a ruling to jail 44-year-old Navalny, sealing his first lengthy prison sentence after a decade of legal battles with Russian authorities.

Navalny was ordered on February 2 to serve the time in a penal colony for breaching his parole terms while he was in Germany recovering from a nerve agent poisoning he blames on the Kremlin.

Supporters of the outspoken opposition figure say the cases are a pretext to silence his corruption exposes and quash his political ambitions.