Russia's prominent jailed opposition figure Alexei Navalny has lost an appeal against a nine-year prison term, but not before launching a scathing attack on the war in Ukraine.

Condemning Vladimir Putin's war as stupid, he said it was "like your courts, built entirely on lies".

Navalny was already serving a jail term when he was convicted in a fraud case rejected by supporters as fabricated.

He addressed the court in Moscow via a video link at his penal colony.

Long seen as a President Putin's most vocal critic in Russia, Navalny was detained the moment he flew home from Germany after treatment for a near-fatal nerve agent attack in Siberia in August 2020.

He was initially jailed for two and a half years for breaking bail conditions while being treated in hospital, but in March he was given an extra nine years for fraud and contempt of court.

The prosecutor told the court the verdict in March had been fair and justified but Navalny's defence lawyer argued it had contradicted international law.

In comments that were repeatedly interrupted, Navalny said he despised the court and said the rulings against him were no different from the lies used by "madman" President Putin and state TV to justify the war.

"You will suffer a historic defeat in this stupid war that you started. It has no purpose or meaning. Why are we fighting a war?" he said.

Russia has silenced criticism of its three-month war in Ukraine, prosecuting dozens of people who have refused to use the term "special military operation" and blocking independent media outlets.

During Tuesday's appeal hearing, Navalny told the court that the judge who gave him his initial jail term in February 2021, Natalya Repnikova, had later told his lawyers she regretted her decision.

Repnikova died months later of coronavirus "according to the official version", he reportedly told the court.

Since Navalny was jailed last year he has been held in a jail at Pokrov, east of Moscow, but he now faces being transferred to a penal colony with a far stricter regime and very limited rights to prison visits.

His colleagues say he is due to be moved to a facility in Melekhovo, where one former prisoner has made allegations of systematic torture.