A Moscow appeal court on Saturday upheld a prison sentence imposed on chief Kremlin critic Alexei Navalny after he returned to Russia from Germany last month.

Judge Dmitry Balashov rejected Navalny's appeal of the February 2 ruling, which turned a 2014 suspended sentence on embezzlement charges into real jail time. 

The judge decided to count six weeks Navalny was under house arrest as part of the time served, so he will now be imprisoned for just over two-and-a-half years in a penal colony.

Navalny, a 44-year-old anti-corruption campaigner who has emerged as President Vladimir Putin's most prominent opponent, was arrested in January when he returned to Russia after months in Germany recovering from a nerve agent poisoning he blames on the Kremlin.

He was detained for violating parole conditions of the 2014 suspended sentence and it was then turned into a custodial sentence.

Navalny and his supporters say the rulings and several other cases against him are a pretext to silence his corruption exposes and quash his political ambitions.

He was due in court again later Saturday in a another trial where he is accused of defamation for calling a World War II veteran a "traitor" after he appeared in a pro-Kremlin video. 

Prosecutors have called for Navalny to be fined the equivalent of $13,000 in that case. They also want his 2014 sentence turned into real jail time because the alleged defamation took place while he was serving the suspended term.