Lawyers acting for Vasily Aleksanyan, the former Yukos executive who is gravely ill with Aids, said they were concerned that Russia’s prison service had not disclosed the location of their client after saying he had been transferred from jail to a clinic.

“We have no idea where he has been taken, and this is particularly alarming, given Vasily’s repeated statements that he has been placed under pressure to give false testimony by investigators,” said Drew Holiner, a lawyer with the European Court of Human Rights (ECHR).