VIENNA, Austria – Fearing air strikes, Iran is using reinforced materials and tunneling deep underground to store nuclear components – measures meant to make the facility resistant to “bunker busters” and other special weaponry, diplomats said yesterday.

The diplomats spoke as a 35-nation meeting of the U.N. atomic watchdog agency ended more than three days of deliberations focusing on Iran and North Korea, which are both accused of seeking to develop nuclear weapons.

Among criticisms of Iran’s nuclear related activities, a review presented at the meeting of the International Atomic Energy Agency faulted Tehran for starting work on the tunnel at Isfahan without informing the agency beforehand.

The review said that – following agency prodding – Iran over the past few months has provided “preliminary design information” on the tunnel in the central city that is home to the country’s uranium enrichment program. It said that construction began in September “to increase capacity, safety, and security of nuclear material.”

Asked for details on the tunnel, a diplomat familiar with Iran’s said that parts of it apparently would run as deep as half a mile below ground and would be constructed of hardened concrete and other reinforced materials.

Other diplomats said on condition of anonymity that such moves were clearly motivated by Iranian concerns of air attacks by America or Israel, which both accuse the Iranians of trying to secretly build nuclear weapons.