Iraq is searching for "highly dangerous" radioactive material that was stolen in November 2015, raising fears it could be used as a weapon if acquired by Islamic State militants, officials say.

Key points: Stolen radioactive material raises security fears

Stolen radioactive material raises security fears Material went missing in November and could be used to make "dirty bomb"

Material went missing in November and could be used to make "dirty bomb" Fears material could be in Islamic State militants' hands

The material, stored in a protective case the size of a laptop computer, went missing from a storage facility belonging to US oilfield services company Weatherford near the southern city of Basra, a ministry document showed.

A spokesman for Iraq's Environment Ministry said he could not discuss the issue, citing national security concerns.

The material, which uses gamma rays to test flaws in materials used for oil and gas pipelines in a process called industrial gamma radiography, is owned by Istanbul-based SGS Turkey, according to the document and officials.

The document, dated November 30 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 belonging to Weatherford in the Rafidhia area of Basra province".

A senior Environment Ministry official based in Basra, who requested anonymity, said the device contained up to 10 grams of Ir-192 "capsules", a radioactive isotope of iridium also used to treat cancer.

The material is classed as a Category 2 radioactive source by the International Atomic Energy Agency, meaning if not managed properly it could cause permanent injury to a person in close proximity to it for minutes or hours, and could be fatal to someone exposed for a period of hours to days.

The harmfulness from exposure is determined by a number of factors such as the material's strength and age, which was not immediately clear.

The ministry document said it posed a risk of bodily and environmental harm as well as a national security threat.

Fears of Islamic State dirty bomb

"We are afraid the radioactive element will fall into the hands of Daesh," said a senior security official with knowledge of the theft, using an Arabic acronym for Islamic State militants.

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

A dirty bomb combines nuclear material with conventional explosives to contaminate an area with radiation, in contrast to a nuclear weapon, which uses nuclear fission to trigger a vastly more powerful blast.

There was no indication the material had come into the possession of Islamic State militants, which seized territory in Iraq and Syria in 2014 but does not control areas near Basra.

The security official, based in Baghdad, said there were no immediate suspects for the theft, but said the initial investigation suggested the perpetrators had specific knowledge of the material and the facility.

"No broken locks, no smashed doors and no evidence of forced entry," he said.

An operations manager for Iraqi security firm Taiz, which was contracted to protect the facility, declined to comment, citing instructions from Iraqi security authorities.

Reuters