TEHRAN - Iran has started moving the machines that enrich nuclear fuel from the central city of Natanz to an underground bunker near the northern city of Qom, its top nuclear official was quoted as saying on Monday.

"Transferring Natanz centrifuges to Fordow (near Qom) is under way with full observance of standards," Fereydoun Abbasi-Davani told state broadcaster IRIB. "Fordow's facilities are being prepared and some centrifuges have been transferred."

Tehran announced in June that it would shift its production of higher-grade uranium to the underground facility in Fordow, in defiance of international calls to halt uranium enrichment which some countries say is aimed at making nuclear bombs, a charge Iran denies.