For years, the Iranians have refused to answer questions raised by the inspectors about what the I.A.E.A. delicately calls “possible military dimensions” of the Iranian program — evidence that some work has been conducted on warhead designs, trigger devices and similar technologies that strongly suggest that the country is contemplating using its fuel for weapons.

The White House, which has been trying to increase the economic pressure on Iran while trying to dissuade Israel from attacking Iran’s nuclear facilities, characterized the newest report as more evidence of Iranian defiance. “Iran has continued to pursue its uranium enrichment program in violation of multiple United Nations Security Council resolutions without demonstrating any credible or legitimate purpose for doing so,” the National Security Council spokesman, Tommy Vietor, said on Friday. “When combined with its continued stonewalling of international inspectors, Iran’s actions demonstrate why Iran has failed to convince the international community that is nuclear program is peaceful.”

Despite the I.A.E.A.’s findings at Fordo, American officials insist that Iran’s overall progress has been halting at best. The report also shows that despite Iran’s repeated boasts, it is still having trouble using a significant amount of next-generation equipment to make fuel. The United States also argues, in anonymous interviews and in conversations with Israeli officials, that Iran’s program has a number of vulnerabilities that could be exploited should it decide to try to develop a bomb. American intelligence officials say they do not believe that Iranian leaders have made that decision, though Israeli and British intelligence disagree.

When President Obama and other Western leaders first made public the discovery of the new facility in 2009, American officials said they believed that its exposure meant it would never be used. However, the report on Friday indicated that 696 centrifuges — the tall, silvery machines that enrich uranium by spinning it at supersonic speeds — have been installed. An additional 2,088 have been partially installed, meaning the facility is approaching its design capacity.

The 11-page report also described how Iran has refused, in two separate meetings with inspectors, to answer questions raised in the I.A.E.A.’s last report, issued in November, about experiments that could be linked to work on nuclear weapons. Inspectors were told they could not visit a military site called Parchin, where the inspectors suspect that work was done on conventional explosives that can be used to trigger a warhead. “Iran stated that it was still not able to grant access to that site,” the report said.