The International Atomic Energy Agency (IAEA) assessment "is a laundry list of Iran’s continued defiance of the international community and shows that Iran’s leaders are only furthering the isolation of the Iranian people," said White House national security spokesman Gordon Johndroe.
The IAEA said in a newly released report that Iran still defies a UN call in March to stop uranium enrichment work that can provide fuel for civilian nuclear reactors but also make atomic bomb material.
The report may set the stage for additional sanctions against the Islamic Republic, which denies charges from Washington that it is using its civilian nuclear program as cover for developing atomic weapons.
The UN Security Council’s five permanent members plus Germany are dispatching European Union foreign envoy Javier Solana for new talks as early as next week with Iranian nuclear negotiator Ali Larijani, a US official said.
US Under Secretary of State Nicholas Burns said Solana would renew a year-old offer from the international community for Iran to suspend its uranium enrichment in return for cooperation on civil nuclear energy.
"Should it turn down the offer again, I would think what you’d see is a strong drive by the US and all the other members of the current five … for a third (UN) sanctions resolution," he told the Heritage Foundation.
Countries might also go beyond the Security Council to "enact even tougher measures" against Iran, Burns added without elaborating.
"Iran is once again thumbing its nose at the international community. Iran is out of compliance," the top US official said.
The UN watchdog’s report came out amid a dispute pitting the United States against IAEA director Mohamed ElBaradei, who advocates letting Iran keep some enrichment work.
"We would disagree with anyone who would say that we should throw in the towel," Burns said, adding there was "no possibility" of the Security Council members and Germany abandoning their calls for Iran to stop its nuclear drive.
At an underground facility in Natanz, Iran is feeding 1,312 centrifuge machines with the uranium gas need to make enriched uranium, said the confidential report by ElBaradei, a copy of which was obtained by AFP.
Iran could reach its goal of industrial scale production with 3,000 centrifuges running by the end of June, a senior official close to the IAEA said.
In its report, the IAEA also said its ability to monitor Iran’s nuclear program had "deteriorated" due to lack of access.