Russian opposition politician Vladimir Kara-Murza, jailed for 25 years on treason charges and for denouncing Moscow's Ukraine offensive, has arrived to serve his sentence at a maximum-security Siberian prison, his lawyer said Sunday.
Kara-Murza — a dual Russian-British citizen — was handed the unprecedentedly long sentence in April, with international leaders and supporters calling for his release.
"Vladimir Kara-Murza has been brought to the Omsk maximum security penal colony IK-6 to serve his punishment," his lawyer Vadim Prokhorov said on Facebook.
"He was straight away placed in an isolation cell."
Omsk is some 2,700 kilometres east of Moscow.
Russia's penal system often takes weeks to bring prisoners to the country's far-flung jails, with the whereabouts of a prisoner in transit often unknown and stopping in various jails along the way.
"The whole journey from Moscow to Omsk in the 21st century took no less than three weeks," Prokhorov said, saying he was kept for "several days" in an isolation cell in the central city of Samara.
Prokhorov said placing the 42-year-old in such cells puts his fragile health at risk.
Kara-Murza's lawyers and family have said he suffers from a nerve condition called polyneuropathy due to two poisoning attempts.
Kara-Murza was found guilty of spreading "false information" about the Russian army and of having links to an "undesirable organization" in a closed-door trial in Spring.
His sentence is the longest against a Russian opposition figure in recent years.
He has long campaigned for Western countries to place sanctions on Russian officials.
Moscow has unleashed an unprecedented crackdown on dissent as its troops fight in Ukraine.