The material, stored in a protective case the size of a laptop, went missing from a US-owned storage facility in Basra last November, according to leaked environment ministry documents.

An unnamed senior security official with knowledge of the theft said: “We are afraid the radioactive element will fall into the hands of Daesh (Isis).

“They could simply attach it to explosives to make a dirty bomb”.

The document, dated 30 November and addressed to the ministry’s Centre for Prevention of Radiation, describes “the theft of a highly dangerous radioactive source of Ir-192 with highly radioactive activity belonging to SGS from a depot…in the Rafidhia area of Basra province”.