U.S. intelligence agencies hit paydirt several years ago when they searched for a hidden Iranian uranium-enrichment site, spotting telltale signs of digging outside the holy city of Qom.
Iran had already owned up to its first uranium enrichment facility near Natanz in 2002 and U.S. intelligence officials figured it was Iran's only attempt to secretly refine fuel for a nuclear reactor, and possibly a nuclear bomb.
Analysts pinpointed the second site several years ago carved into a mountain near Qom, a Shiite holy city and a religious nerve center of the Iranian regime, according to U.S. officials.
There were multiple streams of intelligence that proved fruitful, but one clear sign produced by spy satellites was evidence of digging for underground facilities, said a senior U.S. intelligence official. That official and other administration officials spoke on condition of anonymity to discuss the sensitive information.
Making the case
U.S., British and French intelligence agencies had been sitting on their evolving intelligence for several years, waiting for construction at the site to progress far enough to prove Iran intended to use it for illegal weapons work. In recent months, Obama administration officials said, equipment had been moved into the new site, making the case against Iran clearer.
The underground facility, a cluster of 3,000 connected centrifuges, was within a few months of being completed when Iran made the surprise disclosure of the site on Monday to the International Atomic Energy Agency, the nuclear watchdog.
A senior administration official said Saturday that Tehran made the disclosure because it learned the site had been discovered.
Although there was no confirmation from the U.S. or Iran, images produced both by DigitalGlobe and GeoEye's commercial fleet of satellites show what independent imagery analysts believe to be the site on a military base near Qom.
According to defense consultancy IHS Janes, which analyzed GeoEye's imagery, the images show a well-fortified facility built into a mountain about 20 miles northeast of Qom, with ventilation shafts and a nearby surface-to-air missile site. The image was taken this week.
A separate analysis was done by GlobalSecurity.org of images taken earlier — between 2005 and January 2009 — by DigitalGlobe and also from Google. Those images were taken during an earlier phase of construction and Globalsecurity.org believes there is no underground site.
Instead, GlobalSecurity.org believes that the probable centrifuge facility is simply built into a cut in a mountain. It is constructed of heavily reinforced concrete and is about the size of a football field, large enough to house 3,000 centrifuges.
Chain of events
Iran's Foreign Ministry, however, gave a different location for the site, saying Monday it was near the village of Fordo, which is about 30 miles south of Qom.
The Iranians' disclosure triggered a fast-moving chain of events, leading to a series of secret intelligence briefings about the enrichment site last week by U.S. officials to Russian and Chinese leaders in New York, the IAEA in Vienna and congressional leaders in Washington.
The administration had intended to confront the Iranians about the secret site later this year, but Tehran's sudden disclosure forced their hand. Now the administration hopes to use the new site as leverage to win a commitment from Iran to abandon its nuclear program or face severe new economic sanctions.
Diplomacy and economic pressure are the intended way ahead. Defense Secretary Robert Gates said Sunday that a military strike against Iran's nuclear infrastructure would be ineffectual, delaying Iran's program by one to three years at most.
"This is part of a pattern of deception and lies on the part of the Iranians from the very beginning with respect to their nuclear program. So it's no wonder that world leaders think that they have ulterior motives, that they have a plan to go forward with nuclear weapons. Otherwise, why would they do all this in such a deceptive manner?" Gates said Sunday in an interview on ABC's "This Week."
Site guarded by elite troops
Secretary of State Hillary Clinton said Sunday that Iran has until Thursday to agree to inspections and voluntarily halt its hidden nuclear program, or the United States and its allies will seek crippling sanctions.
Senate Intelligence Committee Chairman Sen. Dianne Feinstein, D-Calif., said Sunday that Tehran's intention to produce weapons-grade uranium in the Qom facility has not yet been proven, but the indications are strong.
Clinton spoke on CBS' "Face the Nation." Feinstein appeared on "Fox News Sunday."
U.S. officials said the site was secret and guarded by elite Iranian troops. And there are too few centrifuges to play a meaningful role in Iran's civilian energy program.
However, there are enough centrifuges to refine a small amount of uranium suitable for a warhead, according to U.S. intelligence and administration officials.
President Barack Obama and his senior aides began moving quickly to deal with Iran's disclosure on Tuesday night in New York as they readied for the United Nations General Assembly meeting and sessions with world leaders.
Influence over Iran
Obama and the U.S. officials debated into the night over what intelligence they could share with the IAEA and other U.S. allies, as well as China and Russia. The two superpowers wield considerable influence over Iran, and their support would be needed to win U.N. Security Council sanctions. China, particularly, supplies Iran with equipment and technology for its oil and gas industry.
Obama personally informed Russian President Dmitry Medvedev on Wednesday. Lower-level American and Russian officials discussed the matter throughout the day Thursday. White House officials told their Chinese counterparts on Wednesday.
Also Wednesday, IAEA officials in New York were briefed about the site, followed by a detailed briefing delivered in Vienna on Thursday afternoon.
At the same time, White House officials began briefing House and Senate leaders and key committee members.
The United States, France and United Kingdom went public with their intelligence on the Iranian site on Friday.
Iran maintains the Qom facility is an experimental site for its civilian nuclear program. Iran is bound by an IAEA agreement to disclose new nuclear sites when construction begins. But Iran declared in March 2007 that it rejected that IAEA requirement.
Iran says its new site is meant to produce uranium refined to contain 5 percent of the radioactive isotope U-235, well below the 90 percent needed to fuel a warhead.
The centrifuges at the original Iranian site at Natanz produce about 2 kilograms a day of low-enriched uranium suitable for fueling a civilian nuclear reactor. Iran has accumulated about 1,400 kilograms of low-enriched uranium.
Depending on the design, a warhead needs 12 to 25 kilograms of highly enriched uranium, but U.S. intelligence has reported that Iran has not yet produced any highly enriched uranium.
The U.S. government continues to stand by its judgment from 2007 that Iran could have a nuclear bomb within one to five years.