IAEA: Iran Burying Nukes Against Attack (March 4, 2005)
"Iran is using reinforced materials and tunneling deep underground to store nuclear components - measures meant to deter "bunker busters" and other special weapons in case of attack, diplomats said Thursday."
(snip)
"Asked for details on the tunnel, a diplomat familiar with Iran's dossier said parts of it apparently would run as deep as half a mile below ground and would be constructed of hardened concrete and other special materials meant to withstand the severest of air attacks." 
DigitalGlobe imagery from 21 July 2004 Construction is proceeding, especially in Zone B of the Technology Center (Note that this facility broke ground in 1995)
