The office of Prime Minister Benjamin Netanyahu reported Friday that during a meeting with Representative Mike Rogers, a Michigan Republican who heads the intelligence committee, Mr. Netanyahu said, “Just yesterday, we received additional proof of the fact that Iran is continuing to make accelerated progress toward achieving nuclear weapons while totally ignoring international demands.” He appeared to be referring to news accounts about the inspectors’ report.

Iran’s top negotiator was in Vienna at the International Atomic Energy Agency’s headquarters in an effort to work out an agreement for Iran to allow inspectors to visit a site, called Parchin, where inspectors believe weapons work may have been conducted. But the effort failed, along with parallel efforts to get Iran to answer a series of questions about suspected weapons-related experiments that the country has refused to discuss for several years.

An administration official, who declined to speak for attribution about intelligence matters, confirmed that in the American assessment, “the numbers of centrifuges being installed and operating” at the Fordow plant, which he characterized as “a few hundred,” would “add to Iran’s ability to produce more 20 percent low-enriched uranium.” That purity can be converted relatively rapidly to bomb-grade fuel, a process called “breakout.” But, the official added, “Any breakout would not be a quiet affair: the I.A.E.A. is in the facility regularly and they would detect a move” to build a weapon. He concluded that while the work at Fordow was a violation of United Nations Security Council resolutions, “it is also not a game-changer.”

Iran insists that the 20 percent enrichment is for a reactor that produces medical isotopes. But it has already produced far more of the 20 percent uranium than is needed to fuel that reactor for many years.