Vladimir Kara-Murza, Jr., an activist and journalist who twice survived poisonings he blamed on Russian authorities, has rejected the charges against him as punishment for standing up to President Vladimir Putin and likened the proceedings to the show trials under Soviet dictator Josef Stalin.

Human rights organizations and Western governments denounced the verdict and demanded his release. Amnesty International declared the 41-year-old to be a prisoner of conscience.

The charges against Kara-Murza, a dual Russian-British citizen who has been behind bars since his arrest a year ago, stem from a March 2022 speech to the Arizona House of Representatives in which he denounced Russia’s invasion of Ukraine, along with other speeches abroad.

Days after that invasion, Russia adopted a law criminalizing spreading “false information” about its military. Authorities have used the law to stifle criticism of what the Kremlin calls “a special military operation.”

The sweeping campaign of repression is unprecedented since the Soviet era, effectively criminalizing independent reporting on the conflict and any public criticism of the war.

Last month, a Russian court convicted a father over social media posts critical of the war and sentenced him to two years in prison. His 13-year-old daughter, who drew an antiwar sketch at school, was sent to an orphanage. Days later, Russia’s security service arrested Evan Gershkovich, an American reporter for The Wall Street Journal, on espionage charges.

In a statement at the end of his trial, Kara-Murza said that he was jailed for “many years of struggle against Putin’s dictatorship,” his criticism of the war in Ukraine and his long efforts to champion Western sanctions against Russian officials involved in human rights abuses.

“I know that the day will come when the darkness engulfing our country will dissipate,” the father of three told the court in remarks that were posted on his Twitter account. “This day will come as inevitably as spring comes to replace even the frostiest winter.”

Kara-Murza reacted calmly as the judge read the verdict and sentence in a quick monotone. His lawyer, Maria Eismont, later quoted him as telling her: “My self-esteem has risen: I realized that I have done everything right. Twenty-five years is the highest appraisal that I could get for doing what I did and what I believed in, as a citizen, a patriot and a politician.”

Kara-Murza was an associate of Russian opposition leader and fierce Putin critic Boris Nemtsov, who was assassinated near the Kremlin in 2015. Kara-Murza survived poisonings in 2015 and 2017 that he blamed on the Kremlin. Russian officials have denied responsibility.

Another prominent opposition figure, Ilya Yashin, was sentenced to 8½ years in prison late last year on charges of discrediting the military.

Amnesty International denounced Kara-Murza’s sentence as “yet another chilling example of the systematic repression of civil society, which has broadened and accelerated under the Kremlin since Russia’s invasion of Ukraine last year.”

“The so-called ‘crimes’ Vladimir Kara-Murza was tried for — speaking out against the invasion and advocacy on behalf of victims of human rights violations — are in fact acts of outstanding bravery,” Amnesty’s Russia Director, Natalia Zviagina, said in a statement. “This verdict wrongly conflates human rights activism with ‘high treason’ and is reminiscent of Stalin-era repression.”

The group declared Kara-Murza a prisoner of conscience, convicted solely for his political beliefs, and demanded his immediate and unconditional release.

Memorial, one of Russia’s oldest and most prominent human rights organizations that was named a co-winner of the 2022 Nobel Peace Prize along with human rights defenders from Ukraine and Belarus, also has named Kara-Murza as a political prisoner.

Memorial’s head Yan Rachinsky described the sentence as “monstrous,” adding that it reflected the authorities’ fear of criticism and “marked a difference between today’s Russia and civilized countries.”

The British, American, German and other Western governments strongly condemned the conviction.

“Vladimir Kara-Murza bravely denounced Russia’s invasion of Ukraine for what it was — a blatant violation of international law and the U.N. Charter,” British Foreign Secretary James Cleverly said in a statement.

The Foreign Office said it summoned Russian Ambassador Andrey Kelin over the conviction. The British government previously sanctioned the judge presiding at the trial for human rights violations in another case and said it would consider taking further action to hold people accountable in Kara-Murza’s case.

The U.S. State Department hailed Kara-Murza along with jailed Russian opposition leader Alexei Navalny, Yahsin and “many others who serve their country and their fellow citizens at great personal cost by boldly standing up for human rights and fundamental freedoms.” It renewed its call for the release of Kara-Murza and more than 400 other political prisoners in Russia.

The U.N. Human Rights Chief Volker Türk called the sentence “another blow to the rule of law and civic space in the Russian Federation.”

Kremlin spokesman Dmitry Peskov refused to comment.

Kara-Murza’s health has deteriorated in custody, leading to the development of polyneuropathy — disease of or damage to nerves — in both his feet, according to his lawyers.