The Times said a confidential report by the U.N.'s International Atomic Energy Agency showed Iran has done research and testing on components of a nuclear weapon, but does not indicate how close the country might be to making a weapon.
The report, titled "Possible Military Dimensions of Iran's Nuclear Program," emphasizes the conclusions remain tentative, subject to confirmation of evidence, which has come from intelligence agencies and the U.N.'s own investigations.
The report describes a detailed Iranian program, apparently begun in 2002, "aimed at the development of a nuclear payload to be delivered using the Shahab 3 missile system," which is capable of striking targets in parts of Europe and in the Middle East.
U.S. officials said that during the course of negotiations with Iran, which began last week, Iran must give international inspectors full access to all its nuclear sites. The sites include an underground uranium-enrichment center being built at a military base near Qum, that Iran revealed 10 days ago, but denies is being used for weapons development.
Last week, Iran said it would permit international inspectors to visit the site this month, even though it has denied such access to the site and to other information over the last three years.
The U.N. report says "Iran has sufficient information to be able to design and produce a workable implosion nuclear device" and has enriched uranium for that purpose.
The report suggests Iran has done research and has made high-voltage detonators, fired explosives and designed warheads to develop nuclear arms, although Iran says that its scientists have never conducted researched how to create a warhead.