LONDON — Iraq has notified the United Nations that Sunni militants seized nuclear material from a university in the northern city of Mosul last month as they advanced toward Baghdad, the nuclear regulatory body of the United Nations said Thursday.

Gill Tudor, a spokeswoman for the International Atomic Energy Agency, which is based in Vienna, said in a statement that the organization’s experts believed that the material — thought to be uranium — was “low grade and would not present a significant safety, security or nuclear proliferation risk.”

Word of the seizure first emerged in a letter to the United Nations dated Tuesday and seen by reporters from Reuters, which quoted it as saying that “terrorists” from the insurgent Islamic State in Iraq and Syria had taken control of the materials.

The letter said that almost 90 pounds of uranium compounds had been kept at the university and that the materials “can be used in manufacturing weapons of mass destruction,” Reuters said.