Baghdad- Iraq today warned the UN that Sunni militants had seized nuclear materials used for scientific research at a university in the city of Mosul. In a letter seen by sources, Iraq's envoy to the UN said nearly 40kg (88lb) of uranium compounds were seized. The letter appealed for international help to "stave off the threat of their use by terrorists in Iraq or abroad." US officials reportedly played down the threat, saying the materials were not believed to be enriched uranium. The officials added that it would be difficult for the rebels to use the materials to make weapons. "Terrorist groups have seized control of nuclear material at the sites that came out of the control of the state," Ambassador Mohamed Ali Alhakim said in the letter. "These nuclear materials, despite the limited amounts mentioned, can enable terrorist groups, with the availability of the required expertise, to use it separately or in combination with other materials in its terrorist acts," he added. Mosul, some 400km (250 miles) north-west of Baghdad, was last month seized by Isis-led (Islamic State in Iraq and the Levant) insurgents. The letter comes a day after Iraqi officials confirmed that the rebels were in control of a disused chemical weapons factory. Iraq said the Muthanna complex, north-west of the capital Baghdad, housed remnants of rockets filled with sarin and other deadly nerve agents. The UN and US have said the munitions are degraded and the rebels will be unable to make usable chemical arms from them. In recent weeks, Isis insurgents have seized huge swathes of north-western Iraq. The UN has said at least 2,417 Iraqis, including 1,531 civilians, were killed in "acts of violence and terrorism" in June. More than a million people have fled their homes as a result of the fighting.