The White House says it is closely studying a new UN report on Iran's nuclear program.
The report by the International Atomic Energy Agency (IAEA) says Iran has doubled the number of uranium enrichment machines it has at an underground bunker.
The IAEA said the number of centrifuges at Fordow had more than doubled from 1,064 to 2,140. The IAEA added the new machines were not yet operating.
The report also said Iran had increased stockpiles of nuclear materials.
The IAEA said Iran had produced nearly 190 kilograms of higher-grade enriched uranium since 2010. That's up from 145 kilograms in May.
Iran says it needed the higher-grade fuel for a medical research reactor.
Finally, the IAEA report said high-level talks this year with Iranian officials have resulted in "no concrete results."
White House spokesman Jay Carney said Iran still had a "window of opportunity" to resolve the standoff diplomatically, but that "it will not remain open indefinitely."
"We are closely studying the details of the report, but broadly speaking it is not surprising that Iran is continuing to violate its obligations. As the report illustrates, we are in a position to closely observe Iran's program. And to detect any effort by Iran to begin production of weapons grade uranium," Carney said.
"And, and just to reiterate, the president has made clear frequently that he is determined to prevent Iran from obtaining a nuclear weapon and he has led unprecedented effort to pressure Iran to live up to its obligations. The window of opportunity to resolve this diplomatically remains open but it will not remain open indefinitely."
The White House also repeated that releasing oil from the Strategic Petroleum Reserve in response to high energy prices remains an option but that it had no announcements to make on the topic.
"That remains an option that is on the table, that is something that the G8 made clear back when that meeting was held, because these are obviously issues for the G8 to consider, this is a global market. And that remains the case but I have no announcements to make about that specific option or any other option," Carney said.
In Tehran, Ayatollah Ali Khamenei, Iran's supreme leader, denied his country is seeking to develop nuclear weapons, adding Iran will "never abandon its right for the peaceful use of nuclear energy."
Based on reporting by Reuters and AP