The United States on Friday demanded that Iran confess to trying to make atomic arms, suggesting that anything short of that would doom an International Atomic Energy Agency probe of Tehran's nuclear past.

The call, by Gregory L. Schulte, chief U.S. delegate to the Vienna-based IAEA, appeared to set the bar insurmountably high for the investigation by the U.N. agency's chief, Mohamed ElBaradei, with only about a week left before he reports on its progress. Iran has steadfastly denied ever working on a nuclear weapons program.

Criticizing the "slippery deadline" for the agency probe, Schulte said the "measure for progress is whether Iran fully discloses its past weapons work and allows IAEA inspectors to verify it's halted."

"This," he told reporters, "includes explaining past work on weapons design and weaponization and the role of the Iranian military."

A March 3 meeting of the 35-nation IAEA board will evaluate ElBaradei's efforts to probe Tehran's nuclear past -- including alleged attempts to make weapons.

That probe was to have been completed months ago, but agency officials have privately acknowledged it could drag on even past the board meeting.

Reflecting Western dissatisfaction — and the possibility that ElBaradei's report would fall short of expectations — Britain, France and the United States have begun consulting on a resolution for the March meeting that would "draw a line in the sand" both for the IAEA chief and Iran, said a diplomat accredited to the agency.

The last board resolution referred Iran to the U.N. Security Council in late 2006. Any new resolution would reflect frustration with Russian and Chinese opposition to tough U.N. sanctions on Iran, he said. It would also "reflect that it is the board," and not ElBaradei, who makes decisions on what to do about Iran, the diplomat added.

If ElBaradei's probe is deemed unsatisfactory, the board, through a new resolution "has to report to the Security Council that the agency has done all that it can do, and that it cannot guarantee for the peaceful nature of Iran's nuclear program," said the diplomat, who asked for anonymity because he was not authorized to discuss the issue.

Schulte spoke a day after diplomats told The Associated Press that the U.S. had recently shared new intelligence on alleged Iranian nuclear weapons work. One of them also said that Washington also gave the IAEA permission to confront Iran with at least some of the evidence in an attempt to pry details out of the Islamic republic on the activities.

Over the past two years, the U.S. has already shared with the IAEA material on a laptop computer reportedly smuggled out of Iran. In 2005, U.S. intelligence assessed that information as indicating that Tehran had been working on details of nuclear weapons, including missile trajectories and ideal altitudes for exploding warheads.

After declassification, the U.S. also forwarded intelligence on two other issues. One is the "Green Salt Project," a plan that the U.S. alleges links diverse components of a nuclear weapons program, including uranium enrichment, high explosives testing and a missile re-entry vehicle. The other involves material in Iran's possession that the U.S. contends shows how to mold uranium metal into warhead form.

Two diplomats said on Thursday that the new material forwarded to the IAEA over the past two weeks expanded on the previous information from the Americans, but had no additional details.

Iran is under two sets of U.N. Security Council sanctions for refusing to suspend uranium enrichment, which it started developing during nearly two decades of covert nuclear activity built on illicit purchases and revealed only five years ago.

Since then, IAEA experts have uncovered activities, experiments, and blueprints and materials that point to possible efforts by Iran to create nuclear weapons, even though Tehran insists its nuclear project is peaceful and aimed only at creating a large-scale enrichment facility to make reactor fuel.

Its leaders consistently dismiss allegations that they are interested in enrichment for its other use — creating fissile material suitable for arming warheads.

A recent U.S. intelligence assessment that Iran had a clandestine weapons program but stopped working on it four years ago has hurt Washington's attempts to have the U.N. Security Council impose a third set of sanctions on Tehran for failing to halt enrichment.