Jailed British-Russian dissident Vladimir Kara-Murza has reappeared a day after his family announced he had vanished from his Siberian prison.

Concerns had been raised for the wellbeing of Mr Kara-Murza, who is serving a 25-year sentence for treason due to his opposition to the war in Ukraine, after reports he had been taken from Omsk’s IK-6 prison “in an unknown direction”.

On Tuesday, a letter from Mr Kara-Murza emerged, revealing he had been taken to a different penal colony in the same city as punishment for breaking prison rules by failing to get up when ordered.

In his letter, he said he was being held in solitary confinement in the new prison, IK-7, which is reputed to be a harsher facility than his previous one where, he suggested, authorities believed he had become “too comfortable”.

He added that he had been told he would be held at the new prison for four months, until May 26, but this could change.

Mr Kara-Murza, 42, has been a long-term critic of Vladimir Putin and has survived two poisonings since 2015, which have left him with a form of nerve damage called polyneuropathy.

He was jailed by a Moscow court in April 2023, leading the UK to sanction 11 individuals involved in his case.

His wife, Evgenia Kara-Murza, and anti-Putin campaigner Bill Browder have repeatedly called on the UK Government to take further action, while MPs have said the case shows the need for a dedicated hostage affairs lead within the Foreign Office to secure the release of British citizens detained abroad.

Foreign Office officials said they have repeatedly raised Mr Kara-Murza’s case 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.