Russia's judiciary has confirmed a 25-year prison sentence handed down to Vladimir Kara-Murza, one of most vocal critics of President Vladimir Putin.
The appeal filed by Kara-Murza's lawyers was rejected by a court in Moscow on Monday, state media reported.
The 41-year-old opposition figure was given the harsh sentence in April after being convicted of charges including high treason. The trial was branded a "sham" overseas.
It was the longest jail term ever imposed on a government critic.
Kara-Murza's supporters say the court's ruling amounts to a death sentence due to his ailing health. His lawyer said Kara-Murza lost 17 kilos during pre-trial detention.
Like jailed opposition leader Alexei Navalny, Kara-Murza was also the target of poison attacks. According to his wife, he was diagnosed with severe nerve damage as a result of two poisonings in Russia.
Kara-Murza was detained in April 2022 after returning to Russia from abroad amid a growing Kremlin crackdown on civil society.
Citing investigative circles, state media claimed he helped organizations from NATO countries undermine Russia's national security in return for payment.
He was also accused of discrediting the Russian army, which alone can carry a lengthy jail sentence.
"I am concerned that Vladimir Kara-Murza's only crime was speaking truth to power, for which he is being punished with 25 years in prison," Mariana Katzarova, UN Special Rapporteur on the situation of human rights in Russia, said last week.
