Iraq has informed an international watchdog agency of the theft last November of an industrial radiography device that carries potentially fatal radioactive substances.
Iraqi officials told Reuters that they fear the "highly dangerous" radioactive materials in the device could be used as a dirty bomb or other weapon if acquired by the Islamic State (IS) group, which occupies parts of Iraq.
The International Atomic Energy Agency said on February 17 that Iraq reported the stolen material in November, but had not requested assistance in recovering it.
Reuters reported that the device, used in oil and gas development, was stored in a protective case the size of a laptop computer that disappeared from a storage facility near the southern city of Basra.
While the device belonged to U.S. oil-field-services company Weatherford, the firm said it was not responsible for the theft because it did not "own, operate or control" the bunker where the device was stored.
Iraqi police and intelligence forces are working "day and night" to locate the material, Reuters said.
The U.S. State Department said it was aware of the theft but had seen no sign that IS or other militant groups have acquired it.