Iran agreed not to produce nuclear weapons when it signed the Nuclear Nonproliferation Treaty in 1970, which opened the door for it to acquire civilian reactors. The treaty does not prohibit Iran from producing or possessing enriched uranium but requires it to submit its nuclear facilities to international monitoring to ensure that materials are not diverted to weapons use.
Iran has permitted inspections of its declared commercial nuclear facilities. But last year, an Iranian exile group pinpointed a secret underground enrichment plant outside Natanz, a small mountain town about 200 miles south of Tehran known for its bracing climate and fruit orchards.
In December, the Institute for Science and International Security, a small think tank in Washington, published satellite photos of Natanz from the archives of a commercial firm, DigitalGlobe. The photos showed large-scale construction inside the perimeter of a security fence. Among the buildings were a pilot centrifuge plant and two underground halls big enough for tens of thousands of centrifuges, the institute said.
Pressure mounted to allow international monitors into Natanz, and senior IAEA officials visited the plant in February. They found 160 assembled centrifuges and components for 1,000 more. Moreover, the equipment was to be housed in bunkers 75 feet deep, with walls 8 feet thick.
The level of centrifuge development at Natanz already reflects thousands of hours of testing and advanced technological work, experts said. By comparison, Iraq had tested a single centrifuge for about 100 hours when IAEA inspectors began dismantling Baghdad's nuclear weapons program after the 1991 Persian Gulf War.
"They are way ahead of where Iraq was in 1991," said a U.N. official who is familiar with both programs.
Once it is up and running, Natanz could make enough material for a bomb within a year and eventually enough for three to five bombs a year, experts said.
The Iranian exile group also revealed a secret site near Arak, a city of 400,000 in western Iran known as a historic center for weaving fine Persian carpets. Under international pressure, Iran conceded in February that it plans to build a special type of reactor there that will generate plutonium for research. Plutonium is the radioactive material at the heart of some of the most powerful nuclear bombs.
The disclosures cast previous Iranian government statements in a new light.
Hashemi Rafsanjani, head of an influential government council and president of Iran from 1989 to 1997, gave a speech on Dec. 14, 2001, that has been interpreted widely as both a signal that Iran wants nuclear weapons and a threat to use them against Israel. Describing the establishment of the Jewish state as the worst event in history, Rafsanjani warned, "In due time the Islamic world will have a military nuclear device, and then the strategy of the West would reach a dead end, since one bomb is enough to destroy all Israel."
Rafsanjani has since stepped back in his rhetoric, noting in a sermon on Friday that "because of religious and moral beliefs and commitments that the Koran has created for us, we cannot and will not pursue such weapons that destroy humanity."
On July 20, Iran unveiled a missile based on a North Korean design that brings Israel within range and hailed the event as an important step in protecting the Palestinians. Experts said the new missile could be armed with a small nuclear warhead, and Iran is developing a version that will carry a heavier payload.
"Today our people and our armed forces are ready to defend their goals anywhere," Ayatollah Ali Khamenei, Iran's supreme leader, said in a ceremony unveiling the missile.
Many outside experts as well as Iranians say that even reformers linked to Iranian President Khatami believe that Iran needs a deterrent against its nuclear neighbors -- Israel, Russia and Pakistan -- and possibly against the United States.
"These weapons would guarantee the territorial integrity and national security of Iran," Nasser Hadian, a professor at Tehran University who is aligned with the reformers, said in a telephone interview from New York, where he is teaching at Columbia University. "We feel that we cannot possibly rely on the world to provide security for us, and this is felt by all the factions."
At a symposium in Rome in early July, ElBaradei told the audience that stopping the spread of nuclear, chemical and biological weapons depends greatly on eliminating the incentives for states to possess them. "It is instructive that the majority of the suspected efforts to acquire WMD are to be found in the Middle East, a hotbed of instability for over half a century," he said.
A senior U.N. official said he is not sure that Iran is developing a bomb. But the different fates of Iraq and North Korea, the other members of what Bush called the "axis of evil," demonstrate why countries out of favor with the United States might want a nuclear weapon, he added.