ISIS Militants, Mosul A fighter of the Islamic State of Iraq and the Levant (ISIL) holds an ISIL flag and a weapon on a street in the city of Mosul, on June 23, 2014. Photo: Reuters

In a letter to U.N. Secretary-General Ban Ki-moon obtained by Reuters on Wednesday, Iraq's U.N. Ambassador Mohamed Ali Alhakim said insurgents in Iraq have taken nuclear material from Mosul University. Alhakim pleaded for help to "stave off the threat of their use by terrorists in Iraq or abroad."

"Terrorist groups have seized control of nuclear material at the sites that came out of the control of the state," Alhakim wrote.

Mosul University was housing almost 88 pounds of uranium for scientific research. Alhakim claims it "can be used in manufacturing weapons of mass destruction."

"These nuclear materials, despite the limited amounts mentioned, can enable terrorist groups, with the availability of the required expertise, to use it separate or in combination with other materials in its terrorist acts," he added.

Fears that Iraq was in possession of weapons of mass destruction helped spark the U.S. invasion of Iraq in 2003. Those tales proved to be unfounded. On Wednesday, U.S officials told Reuters they do not believe the substance reportedly seized by insurgents is weapons-grade. In order for the uranium to be used as a weapon, it needs to enriched, a heavily complicated process.

While Alhakim did not specify which group seized the stockpiles, the city of Mosul was taken over by a Sunni extremist group, Islamic State of Iraq and Syria (ISIS) in June. Since then they have taken over several other cities in the country.

Tuesday, a letter made public at the United Nations claimed that ISIS captured a facility near Baghdad stocked with sarin-filled rockets left over from the reign of Saddam Hussein.

The U.S., however, did not see it as a threat. “Whatever material was kept there is pretty old and not likely to be able to be accessed or used against anyone right now,” U.S. Defense Department spokesman Rear Adm. John Kirby told the New York Daily News.