The U.N. atomic agency said on Thursday it believed nuclear material Iraq said had been seized by insurgents was "low grade" and did not pose a significant security risk, Reuters reported.
Iraq told the United Nations in a July 8 letter that the nuclear materials had been taken from a university in the country's north. It appealed for help to "stave off the threat of their use by terrorists in Iraq or abroad".
Al Qaeda offshoot, the Islamic State in Iraq and the Levant, took over swathes of Syria and Iraq before renaming itself the Islamic State on June 29 and declaring its leader caliph - a title held by successors of the Prophet Mohammad.
The International Atomic Energy Agency (IAEA) "is aware of the notification from Iraq and is in contact to seek further details", IAEA spokeswoman Gill Tudor said.
"On the basis of the initial information we believe the material involved is low grade and would not present a significant safety, security or nuclear proliferation risk," she said. "Nevertheless, any loss of regulatory control over nuclear and other radioactive materials is a cause for concern."
Iraq's U.N. Ambassador Mohamed Ali Alhakim told U.N. Secretary-General Ban Ki-moon in the letter that nearly 40 kg (88 pounds) of uranium compounds were kept at Mosul University.
"Terrorist groups have seized control of nuclear material at the sites that came out of the control of the state," he said.
However, a U.S. government source said the materials were not believed to be enriched uranium and therefore would be difficult to use to manufacture into a nuclear weapon.
Olli Heinonen, a former IAEA chief inspector, said that if the material came from a university it could be laboratory chemicals or radiation shielding, consisting of natural or depleted uranium.
"You cannot make a nuclear explosive from this amount, but all uranium compounds are poisonous," Heinonen told Reuters. "This material is also not 'good' enough for a dirty bomb."
In a so-called "dirty bomb", conventional explosives are used to disperse radiation from any radioactive source, such as from hospitals and factories which are less well protected.
Citing U.N. investigations dating back ten years or more, Heinonen said there should be no enriched uranium in Mosul. The Vienna-based IAEA helped dismantle Iraq's clandestine nuclear program in the 1990s - during Heinonen's three decades there.
Any loss or theft of highly enriched uranium, plutonium or other types of radioactive material is potentially serious as militants could try to use them to make a crude nuclear device or a "dirty bomb", experts say.
Because radioactive material is less hard to find and the device easier to make, experts say a "dirty bomb" - which could cause panic and have serious economic and environmental consequences - is a more likely threat than an actual atom bomb.