WASHINGTON – Seven years ago, when Iran revealed the existence of its first secret uranium enrichment site at Natanz, U.S. intelligence agencies had a hunch it wouldn't be Iran's last attempt to illicitly produce fuel that might one day power a nuclear warhead.
So the agencies started looking and, several years ago, hit pay dirt, literally: It pinpointed a second site hidden inside a mountain near Qom, a Shi'ite 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 the telltale digging of 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.
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.
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."
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.
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 two 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.