The Opposition leader has been behind bars since January 2021 on charges of fraud. The US has described the legal process as a "sham" while human rights groups have decried his treatment in prison.

A Russian court on Tuesday rejected Kremlin critic Alexei Navalny's appeal against his nine-year prison sentence for fraud.

The Opposition leader will now be transferred from a penal colony to a high-security prison for serious criminals.

Navalny was arrested in January 2021 upon returning from Germany, where he had been recuperating since the summer of 2020 after being poisoned by a nerve agent — an incident he blames on the Kremlin.

Authorities said the six months of recovery abroad violated the terms of a 3 1/2-year suspended sentence for the misappropriation of funds.

Rights groups decry torture in prison

In March, Navalny was found guilty of fraud and embezzlement, as well as contempt of court. A judge also ordered him to pay a fine of 1.2 million rubles (about $11,500 or €10,400).

The sentence was based on an allegation that he defrauded supporters by seeking donations to run for president.

Navalny and his supporters have decried the charges as politically motivated while rights groups have supported the 45-year-old's report of being tortured in prison.

German and US support for Navalny

The German government has previously called for his release while the United States has called the legal process "a sham."

In Russian prisons for serious offenders, inmates are rarely allowed to meet relatives, receive parcels and letters, or go outside for fresh air.

Navalny's spokesperson, Kira Yarmysh, tweeted that the "maximum-security penal colony where he is to be transferred is notorious for its prisoners being tortured and killed."

The affirmation of his sentence on Tuesday, along with a transfer that does not yet have a fixed date, comes as Russia pushes on with its military offensive in Ukraine and Moscow seeks to muzzle any remaining government critics.