Russian opposition leader Alexei Navalny claims he's facing an extra 15 years in prison.
Navalny is currently serving out a nine-year term after being found guilty of swindling charges in March.
In a Twitter thread today, the anti-corruption campaigner said more charges have been filed against him which could see him spend another 15 years behind bars.
Prosecutors allege he "created an extremist group to incite hatred against officials and oligarchs", he said.
The statement reads: "Not even eight days have passed since my nine-year high-security sentence came into force, and today the investigator showed up again and formally charged me with a new case.
"It turns out that I created an extremist group in order to incite hatred towards officials and oligarchs. And when they put me in jail, I dared to be disgruntled about it and called for rallies.
"For that, they're supposed to add up to 15 more years to my sentence."
There was no immediate confirmation of the new charges.
Human rights organisations and Western politicians have condemned the various criminal cases launched against Navalny, who is Putin's most high-profile opponent, in recent years.
In 2020, Navalny was poisoned with a nerve agent during a campaigning trip in Siberia, according to analysis conducted by multiple European medical institutions. After months of medical treatment in Germany, he was arrested for parole violations when he returned to Russia at the start of 2021.
The campaigner was jailed for two-and-a-half years for breaching the terms of a suspended sentence and other parole violations before the fraud judgment was handed down in March.
Following the invasion of Ukraine, the Kremlin has accelerated its decades-long campaign to quash and silence Russia's domestic opposition. Navalny has spoken out against the war, attacking Putin during a court appearance and calling the invasion "stupid" and "built on lies".
Earlier this year Navalny revealed he feared being sent to a "torture" prison notorious for sexual violence to serve out his nine-year term.
Subsequent reports indicated authorities were preparing for him to be moved but his transfer is yet to be confirmed.
The strict regime maximum security penal colony at Melekhovo is known for brutal beatings and the widespread rape of male inmates.
Navalny posted at the time: “My [new] verdict has not yet entered into force, but prisoners from Melekhovo maximum security colony write that they are equipping a 'prison in prison' for me there.”
The prominent activist has said in the past he wants to replace Putin, and that he would win an election if it wasn't rigged in the tyrant's favour.
Independent media outlet Mediazona last year revealed allegations of systematic torture and sexual violence at the facility known as correctional colony No. 6.
Navalny’s press secretary Kira Yarmysh said that while torture is used on prisoners in many Russian colonies, this jail is “a monstrous place even by such insane standards.”
There had been numerous testimonies about the facility, she said.
In March, Navalny - who nearly lost his life when he was poisoned with Novichok - was sentenced to nine years of strict regime prison for 'fraud and insulting the court’.
Last week it emerged the Russian judge who privately apologised to Navalny for jailing him died in "suspicious" circumstances, reports say.
Judge Natalya Repnikova, 50, was responsible for jailing the leading Putin foe in February last year.
But he revealed in a court hearing that she passed him a private note to express her remorse at her role in imprisoning him, and praising him as a “brave man”.
She later died of ‘Covid’ but Navalny believes she may have been assassinated for her honesty in revealing judicial corruption to its most high-profile victim.
A local politician in Moscow suggested she had been killed with novichok, a nerve agent also used to poison Navalny, almost killing him, in an alleged hit by FSB agents.
