In March Ayatollah Mohammed Yazdi, 84, a hardline ally of Mr Khamenei, was elected head of the Assembly of Experts, the religious body responsible for choosing the country’s new Supreme Leader when the position falls vacant.

Western diplomats say that one of Mr Khamenei’s protégés, Sadeq Larijani, the head of Iran’s judicial system and a noted hardliner, is positioning himself to be appointed the new Supreme Leader when the Assembly of Experts comes to make its decision.

Mr Larijani, 54, is the brother of Ali Larijani, Iran’s former chief nuclear negotiator who is now chairman of the Majlis, the Iranian parliament.

He is now reported to be conducting a purge against more moderate ayatollahs who might put their names forward to become the country’s new Supreme Leader.