Top U.S. intelligence officials who briefed reporters said the reactor was weeks or months away from being functional when it was bombed by Israel in September.
The officials said the U.S. military was not involved in the attack, and the U.S. government, although informed in advance, did not provide the green light.
Syria's ambassador to the United States, Imad Moustapha, said in an interview on CNN that the U.S. accusations are "a fantasy" and the Bush "administration has a proven record about fabricating stories about other countries' WMDs."