VIENNA -- Defying international concerns, Iran has resumed clandestine work linked to uranium enrichment, testing equipment, and producing a gas that can be used to make nuclear warheads, diplomats said yesterday.
The diplomats said Tehran has restarted equipment used to make uranium hexafluoride gas, which, when injected into centrifuges and spun, can be enriched to a level high enough to make the weapons.
While Iran seems only to be testing the machinery, it has apparently produced some of the gas as a side effect, said the diplomats, who are either familiar with investigations by the Vienna-based International Atomic Energy Agency or privy to intelligence. Speaking on condition of anonymity, they said they did not know how much hexafluoride was made and when testing resumed.
The move, coupled with disclosures Tuesday that Iran had restarted building centrifuges, heightened concern that Iran was moving toward full uranium enrichment.
In Washington, State Department spokesman Adam Ereli said Iran had launched a direct challenge to the IAEA call to suspend all enrichment-related and reprocessing activities.
''It certainly raises questions about other commitments Iran has made concerning its nuclear program," he said.
Iran dismissed accusations that it is interested in making nuclear weapons, saying its main interest in nuclear power is to generate electricity. But one diplomat said the news was part of a pattern of recent disclosures indicating Iran to be more interested in pressing ahead with suspect nuclear activities than working to dispel worldwide concerns.
IAEA officials had no comment about the disclosures, reported a day after diplomats said Tehran is building centrifuges.
That move alarmed France, Germany, and Britain, which have been seeking a negotiated resolution with Iran, and was likely to move them closer to the United States, which says Tehran wants to make nuclear weapons.
Foreign Minister Joschka Fischer of Germany expressed ''great concern" yesterday about the reported restart of centrifuge construction, and cautioned Iran against making a ''miscalculation."
Separately, diplomats also said Iran is trying to make or buy deuterium gas, a substance that can be used to boost the power of a nuclear explosion.