Jailed Russian opposition politician Alexei Navalny has had an extra 19 years added to his jail term in a criminal case that he and his supporters said had been trumped up to keep him behind bars and out of politics for even longer.

Mr Navalny, 47, President Vladimir Putin’s fiercest domestic critic, is already serving sentences totalling 11-and-a-half years on fraud and other charges that he says are also bogus.

His political movement has been outlawed and declared “extremist”.

A court at his IK-6 penal colony in Melekhovo, about 235 kilometres east of Moscow, brought to a close his trial on six separate charges, including inciting and financing extremist activity and creating an extremist organisation.

The audio feed from the court, where the trial had been held behind closed doors, was so poor that it was practically impossible to make out what the judge was saying.

Journalists were not let into the courtroom, but able to watch proceedings on CCTV from a special media room nearby, although the feed was cut almost as soon as the sentence was pronounced.

Mr Navalny’s team said the judge had added 19 years to his existing terms. State prosecutors had asked for 20.

Dressed in dark prison uniform and flanked by his lawyers, Mr Navalny smiled occasionally as he listened to the judge.

Alexei Navalny (2nd L) and his lawyer Vadim Kobzev (2nd R) attending the verdict. Photo: AAP

The former blogger, lawyer and corruption investigator has cast himself as a political martyr whose aim is to demonstrate to Russians that it is possible to resist Mr Putin, albeit at great cost.

“For a new, free, rich country to be born, it must have parents. Those who want it. Who expect it and who are willing to make sacrifices for its birth,” Mr Navalny said in his closing statement last month.

In a message posted on social media on Thursday (local time), Mr Navalny had predicted he would get a long jail term, but said it hardly mattered because he was also threatened with separate terrorism charges that could bring another decade.

Mr Navalny said the purpose of giving him extra jail time was to frighten Russians, but urged them not to be cowed and to think hard about how best to resist what he called the “villains and thieves in the Kremlin”.

The charges relate to his role in his now defunct movement inside Russia, which the authorities accused of trying to foment a revolution by seeking to destabilise the socio-political situation.

Mr Putin, in power since 1999, is expected to run for another six-year presidential term in 2024. With Russia waging what he calls a “special military operation” in Ukraine and locked in what he describes as an existential battle with the West, Mr Putin says it is vital for the country to remain united.

Mr Navalny, who in the 2010s brought tens of thousands of people onto the streets to oppose Mr Putin’s rule, was detained in January 2021 after returning to Moscow from Germany, where he had been treated for what Western experts said was poisoning by a Soviet-era nerve agent.

The Kremlin, which at one point accused him of working with the CIA to undermine Russia, denied involvement and denies persecuting Navalny.

It has portrayed him as an agent of disruption and says he never represented serious political competition, and that his case is purely a matter for the courts.

Mr Navalny’s supporters cast him as a Russian version of South Africa’s Nelson Mandela who will one day be freed from prison to govern the country.