Family and friends of jailed British-Russian dissident Vladimir Kara-Murza have become increasingly concerned about his fate after he disappeared from a prison colony in Siberia.

Mr Kara-Murza, who has survived two poisonings since 2015, was jailed for 25 years in April 2023 by a Moscow court on charges of treason over his opposition to the war in Ukraine.

He has been held in solitary confinement in a maximum-security penal colony in Omsk for the past four months, but on Monday his wife, Evgenia Kara-Murza, said he has been moved to an unknown location.

Foreign Secretary Lord Cameron said he was “deeply concerned” about Mr Kara-Murza and urged Russia to provide the captive’s lawyers with details about where he is being held.

She said: “Today, I learned that my husband Vladimir Kara-Murza, sentenced to 25 years for denouncing the crimes of the Putin regime, was moved from the maximum security prison colony in western Siberia, where he had been kept in a punishment cell since September 2023, in an unknown direction.

“There are no grounds for his transfer and that makes it even more frightening as my husband is in the hands of the same people who tried to kill him twice, in 2015 and 2017.

“I demand that the Russian government provide us with information about my husband’s whereabouts.”

Mrs Kara-Murza has previously expressed serious concerns about her husband’s health while in prison, saying the attempts on his life have left him with polyneuropathy, a form of nerve damage.

She has also repeatedly called on the Government to do more to help secure the release of Mr Kara-Murza, a British citizen, saying she fears he will die if he is not freed soon.

Bill Browder, a friend of Mr Kara-Murza and head of the Global Magnitsky Justice Campaign, described the removal of the dissident as “pure sadism”.

He said: “As he’s a UK citizen, our Foreign Secretary David Cameron should be using all tools to get Vladimir released. The Government must act decisively before he dies in prison, which will likely happen if he’s not released.”

MPs have also called on the Government to act, including Commons Foreign Affairs Committee chairwoman Alicia Kearns.

Ms Kearns said: “(Russian President Vladimir) Putin’s toying with Vladimir Kara-Murza is a sign of weakness and of how much Putin fears those who represent freedom of thought and will challenge his kleptocracy.

“Kara-Murza is a political prisoner and British citizen; my thoughts go out to his incredible wife, family and friends.

“This is yet another example of Putin’s Russia’s disregard for the rule of law and use of arbitrary detention to deter dissent. The UK must appoint a dedicated national hostage lead to better protect and advocate for British nationals wrongly held abroad.”

The removal of Mr Kara-Murza from the facility in Omsk echoes the treatment of prominent Putin critic Alexei Navalny, who disappeared for several weeks in December before resurfacing in a prison colony in the Arctic.

Lord Cameron tweeted: “Russia must urgently provide Vladimir Kara-Murza’s lawyers with his whereabouts, following reports that he has been moved from Omsk to an unknown location.

“I’m deeply concerned for Mr Kara-Murza – a British national imprisoned in Russia for speaking out against the invasion of Ukraine.

“I stand with his wife, Evgenia, and plan to meet her soon.”

Foreign Office officials said they had regularly raised Mr Kara-Murza’s imprisonment with Russian authorities, including with the Ministry of Foreign Affairs in Moscow on January 19 and during multilateral engagements.

Vowing to continue those efforts, the department said its staff are providing consular support to Mr Kara-Murza’s family and continue to request consular access.

The Foreign Office said it has sanctioned 11 individuals in response to his sentencing and appeal, as well as two individuals “involved in his earlier poisoning”.