Iran is moving its most sensitive nuclear fuel production to a heavily defended underground military facility outside the holy city of Qum, where it is less vulnerable to attack from the air, and, the Iranians hope, against the kind of cyberattack that crippled its nuclear program, according to intelligence officials.

The head of Iran’s atomic energy agency, Fereydoon Abbasi, spoke about the transfer in general terms on Monday to an official Iranian news service. He boasted that his country would produce the fuel in much larger quantities than it needs for a small research reactor in Tehran that produces medical isotopes.

The fact that Iran is declaring that its production will exceed its needs has reinforced the suspicions of many American and European intelligence officials that Iran plans to use the fuel to build weapons or to train Iranian scientists in how to produce bomb-grade fuel.