London ? Allan Nunn May, a British atomic scientist who spied for the Soviet Union, has died at the age of 91, according to obituaries published Friday.

Nunn May died on Jan. 12 in Cambridge, southern England, The Times and the Daily Telegraph reported. They did not give the cause of death.

One of the first Soviet spies uncovered during the Cold War, Nunn May worked on the Manhattan Project and was betrayed by a Soviet defector in Canada. His unmasking in 1946 led the United States to restrict sharing atomic secrets with Britain. It also ignited a search for other spies inside the Manhattan Project.