TEHRAN (Reuters) - Iran has begun moving machines that enrich uranium to an underground bunker near the holy city of Qom, a senior official said, a move likely to fan Western fears of an Iranian advance toward nuclear weapons capability. His announcement was a further sign of the Islamic state's determination to press ahead with enrichment in defiance of international demands that it desist from such activity, which Tehran says will be for peaceful applications only. "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." Iran announced in June that it would shift its production of higher-grade uranium from its main enrichment complex in the central city of Natanz to the subterranean site at Fordow. Iran, the world's No. 5 oil exporter, denies Western accusations it is seeking to develop nuclear bombs, saying its enrichment program is meant solely to provide an alternative source of electricity or isotopes for medicine and agriculture. Iran only disclosed the existence of Fordow to the UN nuclear watchdog in September 2009 after learning that Western intelligence agencies had detected the mountain site. Moving enrichment activity to the underground bunker could offer greater protection against any attacks by Israel or the United States, which have both said they do not rule out pre-emptive strikes to stop Iran getting nuclear weapons. In Vienna, a senior Western diplomat criticized Iran's move. "The announcement calls attention to Iran's continuing refusal to abide by its international obligations, including the UN Security Council's prohibition against Iran installing or operating any centrifuges," the diplomat said. "Iran's provocative behavior reinforces the need to fully implement international sanctions against Iran." The Islamic Republic also said in June that it aimed to triple its capacity to enrich uranium to a higher grade - 20 percent fissile purity - which it says will be used to replenish the fuel stock for a medical research reactor.