Administration officials say that it would still take Iran a year to produce a weapon and that such an attempt would likely be detected by U.N. inspectors. But the IAEA report contained worrisome information on that score, too. Iran is refusing to answer questions about its work on more advanced centrifuges or on plans to construct more enrichment facilities. In June it barred two of the most experienced inspectors, part of a systematic effort to blind the IAEA to its activities. An analysis of the report by the Institute for Science and International Security concluded that Iran may be seeking “to increase its capability to divert nuclear material in secret and produce weapon-grade uranium in a plant unknown to the inspectors or Western intelligence agencies.” If that is the case, economic sanctions are unlikely to prevent it.