"Only North Korea has built this type of reactor in the past 35 years," the document says. Officials would not say how they obtained the images.
U.S. officials said Syria worked during the last year to enclose the entire compound inside a warehouse-like shell, apparently to guard against overhead surveillance. The officials described the intelligence on condition of anonymity.
American analysts became alarmed last year when the Syrians completed a pipeline that enabled them to get water from the nearby Euphrates River for an underground cooling tank, officials said.
"This was good to go," a senior U.S. intelligence official said. "We had to assume they could throw the switch at any time."
Even so, the U.S. case concerning the compound is likely to continue to face skepticism, in part because of lingering credibility problems U.S. intelligence agencies face after their erroneous prewar assessments on Iraq.
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Doubts voiced
In addition, there are questions left unanswered by the evidence disclosed.
Such a reactor requires a large volume of nuclear fuel, said David Albright, a physicist and former weapons inspector who is president of the Institute for Science and International Security in Washington. The Americans' inability to identify any source of fuel "raises questions about when the reactor could have operated, despite evidence that it was nearing completion at the time of the attack."
He also said the United States and Israel weren't able to identify any Syrian facilities to separate plutonium from reactor fuel, a step necessary to build nuclear weapons. The lack of a processing plant "gives little confidence that the reactor was part of an active nuclear weapons program."
A diplomat in Vienna close to the International Atomic Energy Agency, the U.N. watchdog group, quoted Director-General Mohamed ElBaradei's comment in October that countries claiming to have evidence of illicit nuclear activity "should bring it forward, not bomb first and ask questions later."
The White House said Thursday that it would present its evidence to IAEA officials.
A senior European diplomat said Western intelligence services compared notes months ago and concluded that the site was a nuclear facility built with North Korean help.
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'We were used today'
