Jailed Russian opposition activist Vladimir Kara-Murza has been moved to a maximum-security prison in Siberia, several weeks after he was taken from a Moscow detention centre.
He was placed in an isolation cell at the Omsk penal colony, his lawyer says.
Mr Kara-Murza, who has survived two poisonings since 2015, was jailed for 25 years in April accused of treason and lying about the war Ukraine.
His lawyer said conditions in Omsk threatened his client’s health.
The whereabouts of the 42-year-old had been unknown for several weeks.
The charges against him stemmed from a speech he gave to the Arizona House of Representatives, in which he denounced Russia’s invasion of Ukraine.
His sentence is the longest against a Russian opposition figure in recent years.