The International Atomic Energy report issued in Vienna said Tehran is holding back information on high-explosives testing relating to its nuclear programme and it should provide more information on its missile-related activities, Reuters reported.

“I think right now the Iranians have a lot of explaining to do about the IAEA report, which essentially sees them as not cooperating on some very important dark questions that the international community has about their programmes,” Rice told reporters on her plane on the way to an international conference on Iraq in Stockholm, according to the same source.

Teheran had 3,500 uranium enrichment centrifuges working at the Natanz nuclear facility, the report said. Iran has doubled its ability to enrich uranium. Theoretically, enriched uranium could be turned into an atomic bomb as well as into nuclear fuel.

Iran denied the allegations that it was seeking to build a bomb, saying they were “baseless.”

Iran says its nuclear program is aimed at peaceful ends, but the United States and other western countries say it seeks nuclear weapons.

“The Iranians are certainly being confronted with some pretty strong evidence of a nuclear weapons program, and they are being petulant and defensive,” said David Albright, a former weapons inspector who now runs the Institute for Science and International Security, according to the New York Times.

The report also accused Iran of lack of cooperation, especially in answering allegations that the nuclear program may be intended for military use. Iran has dismissed the documents as “forged” or “fabricated.”

“Iran has refused to explain or even acknowledge past work on weaponization ... This is particularly troubling when combined with determined efforts to master the technology to enrich uranium,” Gregory L. Schulte, the chief U.S. delegate to the agency, told the Associated Press.

Iran says its uranium enrichment program is aimed solely at producing fuel for nuclear reactors that generate electricity.