The U.S. urged Iran on Monday to cooperate with a probe into past suspicious nuclear activities but said even full compliance would not be enough to ease international concerns over Tehran's possession of bomb-making technology.

The comments by Gregory L. Schulte, chief U.S. delegate to the International Atomic Energy Agency, came as the IAEA's 35-nation board convened on the first day of a session that will focus on Iran's nuclear dossier.

Ahead of the meeting, diplomats told The Associated Press that IAEA chief Mohamed ElBaradei's approach on Iran is leading to U.S. concerns that he has overstepped his authority — a view that Schulte appeared at pains to dispel by praising ElBaradei's attempts to pry answers out of Tehran.

"The United States ... strongly supports the IAEA's running effort to overcome Iran's refusal to cooperate fully and of course we will welcome any progress about resolving troubling questions about Iran's past nuclear activities," Schulte told reporters.

But even if Iran does give quick and thorough answers to IAEA questions on former programs that could be linked to a weapons program, "cooperation that gives Iran the wherewithal to build nuclear weapons is not enough," Schulte said.

Those comments were an allusion to U.S. concerns that Iran could exploit good will generated by signs it is cooperating on some issues to weaken concerns about its refusal to suspend uranium enrichment, as demanded by the U.N. Security Council.

Ahead of the meeting, diplomats linked to the IAEA suggested that U.S. disenchantment with ElBaradei was at its highest since early 2005. That was when Washington actively considered pushing for his ouster because it considered him too soft on Iran and a drag on attempts to refer the Islamic republic to the U.N. Security Council — something that happened last year.

Faced with majority support for ElBaradei among his agency's 35-nation board, the Americans dropped public opposition, and he was appointed for his third and final term in February 2005.

But U.S. displeasure was again aroused this year.

First, ElBaradei suggested it was too late to expect Iran to scrap its uranium enrichment program — a key demand from Washington, provoking several formal U.S. protests, said diplomats.

Washington accuses Iran of wanting to build nuclear arms — something Iran's supreme leader, Ayatollah Ali Khamenei, denied Sunday, saying his country had "no plans to create this deadly weapon."

In July, ElBaradei's agency displeased the Americans further by signing a deal with Tehran committing the Iranians to end years of stonewalling and answer questions about more than two decades of nuclear activities — most of it secret, and some of it with possible links to a weapons program.

A report to be discussed by the board describes Iran's cooperation under the plan as "a significant step forward." But the U.S. continues to suspect that Iran is exploiting the plan as a smoke screen to deflect attention from its continued defiance of a Security Council ban on enrichment, a potential pathway to nuclear arms.

The diplomats said Washington — and most other Western board members — also feel that ElBaradei overstepped his authority by agreeing to such a deal without consulting the IAEA board.

But publicly, Washington and other nations backing new U.N. sanctions against Tehran have toned down initial criticism over the pact because they have realized that opposition could backfire.