The White House said on Thursday that it was closely studying a UN report that showed Iran has possibly expanded uranium enrichment machines and increased stockpiles of nuclear material.
"We are closely studying the details of the report, but broadly speaking it is not surprising that Iran is continuing to violate its obligations," White House Press Secretary Jay Carney told reporters when asked about the UN International Atomic Energy Agency's quarterly report on Iran. "As the report illustrates, we are in a position to closely observe Iran's program," he said.
The report showed Iran has doubled the number of uranium enrichment machines it has in an underground bunker.
Carney said the U.S. has made it clear to Iran that they have a limited window of time to stop its atomic work and diplomatic terms offered by the Western world will not remain open "indefinitely."
"The president has made clear frequently that he is determined to prevent Iran from obtaining a nuclear weapon," he said. "So long as the Iranian regime refuses to comply with its international obligations, the United States, with its allies, will continue to take actions to further isolate and penalize Iran and the regime."
Meanwhile on Thursday, the Guardian reported that U.S. General Martin Dempsey said that an Israeli attack on Iran would delay but not stop its nuclear program.
"I don't want to be complicit if they (Israel) choose to do it," Dempsey said.
Earlier Thursday, the IAEA released a new report saying Iran has doubled the number of uranium enrichment machines it has in an underground bunker.
The UN International Atomic Energy Agency said in its quarterly report on Iran that the number of centrifuges at Fordo, near the holy Shi'ite Muslim city of Qom, about 130 km (80 miles) from Tehran, had more than doubled to 2,140 from 1,064 in May.
The new machines were not yet operating, it said.
The report showed that Iran had produced nearly 190 kg (418 pounds) of higher-grade enriched uranium since 2010, up from 145 kg in May.
Iran says it needs this material - which is much purer than fuel needed for electricity generation - for a medical research reactor, but it also takes it significantly closer to making potential bomb material.
The IAEA also expressed concerns about Parchin, a military site south of the capital that it wants to inspect for evidence of past nuclear weapons development.
"Significant ground scraping and landscaping have been undertaken over an extensive area at and around the location," it said.
Five buildings had been demolished and power lines, fences and paved roads removed, the report said, "extensive activities" that would hamper its investigation if granted access.
"The activities observed ... further strengthen the agency's assessment that it is necessary to have access to the location at Parchin without further delay", the IAEA said.
Iran says Parchin is a conventional military facility and has dismissed the allegations about it as "ridiculous".
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