At the same time, the State Department said Washington's wholesale rejection of the International Atomic Energy Agency's conclusion -- described by a senior official as "simply impossible to believe" -- did not mean it had decided to press the IAEA board to refer the Iran program to the UN Security Council.
"We're going to be studying it (the IAEA report) and we're going to be taking the action with our Board of Governors colleagues that we think is appropriate," deputy spokesman Adam Ereli told reporters.
"I'm not going to discuss what our view of the conclusions are and what we're going to do because we're still discussing that ourselves," he said.
The IAEA board meets next week in Vienna to consider the report and if it finds Iran to be in violation of the nuclear Non-Proliferation Treatycould refer the matter to the UN Security Council.
Such a referral, which could lead to sanctions, would result in an "international crisis," Iran's representative to the IAEA, Ali Akbar Salehi, said earlier Thursday.
Although Ereli did not repeat the "simply impossible to believe" remark made on Wednesday by John Bolton, the top US diplomat for arms control, he maintained it had not given up on the IAEA.
"I would not go from there to presume a wholesale indictment of the IAEA," he said. "I think the IAEA is doing valuable work."
And, he reiterated the US conviction that Iran is secretly developing nuclear weapons.
"Iran has a nuclear weapons program and has been deceiving the international community about that program for a long time," Ereli said flatly. "It will certainly be interesting to note whether and to what extent the IAEA report documents what we've been saying for many, many years."
The IAEA Thursday rejected Bolton's charges and said it stood by its report, which is to be submitted to its board of governors at a meeting in Vienna November 20.
The document was the result of eight months of investigations, including dozens of trips by inspectors to Iran and intensive laboratory analyses of samples, since director-general Mohammed ElBaradei visited Iran to check out reports of undeclared nuclear facilities.
In it, ElBaradei accuses Iran of covert nuclear activities over the past 20 years, including producing plutonium and enriching uranium, but says there is not yet evidence Tehran is trying to produce an atomic weapon.
Several State Department officials suggested that ElBaradei was trying to please all members of the IAEA board, which includes Iran, by listing Tehran's transgressions but not agreeing with US allegations that the Islamic republic is using its civilian nuclear energy program as cover for weapons development.
"Most UN agency reports are written in such a way as to give everybody something," one senior official said, hinting that the IAEA had included enough damning information in the document for Iran to be punished even without coming to Washington's conclusion.
"(The question is) what can you take away from the report that's actionable?" the official said. "That's the game and we're in the process of deciding how we want to play that game."
"We believe that Iran has a nuclear weapons programs and has had a nuclear weapons program and that conclusions to the contrary fly in the face of what we believe the evidence shows," the official said.
A second department official, speaking to AFP on condition of anonymity, echoed that theme.
"It's the interpretation of the facts, not the facts themselves that we have a problem with," that official said.