The Iraqi Government is seeking international help to prevent the Islamic State of Iraq and the Levant (ISIS) using the nuclear materials they seized from Mosul University.
In a letter obtained by Reuters, Iraq's UN Ambassador Mohamed Ali Alhakim told UN secretary-general Ban Ki-moon that the university had nearly 40kg of uranium compounds for scientific research.
"Terrorist groups have seized control of nuclear material at the sites that came out of the control of the state," Alhakim said, noting that the materials could be used for the production of weapons of mass destruction (WMD), and be smuggled out of Iraq.
"These nuclear materials, despite the limited amounts mentioned, can enable terrorist groups, with the availability of the required expertise, to use it ... in combination with other materials in its terrorist acts," Alhakim added.
However, the US played down the threat, saying the materials were not believed to be enriched uranium.
An unnamed US official told Reuters that it would be difficult to manufacture the materials into a weapon.
The letter comes a day after the Iraqi Government confirmed that the terrorists have assumed control of a non-functioning chemical weapons factory in the north-west of Baghdad, BBC News reported.
Called the Muthanna complex, the facility houses remnants of rockets filled with sarin and other lethal nerve agents, including mustard gas, and is used by UN inspectors to destroy chemical production facilities and equipment.
ISIS, which is an al-Qaeda splinter group, has captured several towns and cities across Iraq's northern and western provinces in the last month.