The visit by about 30 local and foreign journalists to the Natanz uranium enrichment facility, 150 miles south of Tehran, reflected an unusual degree of openness by the Islamic state.
Iran says its nuclear programme is nothing for the world to fear and will only be used to generate much-needed electricity. But Washington and the EU fear Iran could use its nuclear plants to produce bombs and have raised particular concerns that Natanz could be used to make bomb-grade fuel.
Approaching the 1,110-acre site ringed by arid mountains, journalists counted at least 10 anti-aircraft batteries, parts of which have been built deep underground as protection from aerial attack. At the heavily guarded main gate there were no signs to indicate the nature of the sprawling site whose existence was first revealed by an Iranian exile group in late 2002.