Mohamed ElBaradei also criticized Tehran for not accepting an internationally endorsed plan meant to delay its ability to make such weapons.
The unusually blunt comments appeared to be a reflection of frustration four days before he ends his tenure leading an agency that has proven unable to overcome Iran's defiance and ease international concerns that it may be using a civilian nuclear program as a cover for plans to make weapons.
"There has been no movement on remaining issues of concern which need to be clarified for the agency to verify the exclusively peaceful nature of Iran's nuclear program," ElBaradei told the opening session of the IAEA's 35-nation board of governors. "We have effectively reached a dead end, unless Iran engages fully with us."
"Issues of concern" is the IAEA term for intelligence and other information available to the agency indicating that Tehran has experimented with nuclear weapons programs, including missile-delivery systems and tests of explosives that could serve as nuclear-bomb detonators.
Since revelations of a secret Iranian nuclear program surfaced eight years ago, much of ElBaradei's energies have been spent on trying to nudge Tehran to meet international demands that it freeze uranium enrichment and cooperate on other issues meant to ease fears of its nuclear aims.
Iran started stonewalling the agency over a year ago over the "issues of concern," saying there was nothing to investigate because the allegations were false.
ElBaradei has emphasized the need for talks instead of threats in engaging Iran. He has criticized the U.S. for invading Iraq on the pretext that Saddam Hussein had a nuclear weapons program, which has never been proven. That - and perceived softness on the Iran issue - has drawn criticism from the U.S. and its allies that he was overstepping his mandate.
But ElBaradei's comments Thursday left little doubt that - just days before his departure - he was most unhappy with Iran.
"I am disappointed that Iran has not so far agreed to the original proposal" involving removal of most of Iran's enriched stockpile, ElBaradei told the meeting.
Tehran's approval "would greatly help to alleviate the concerns relating to Iran's nuclear program," he added.
The plan approved by the six world powers negotiating with Iran over the past few months would commit Tehran to ship out 70 percent of its enriched uranium for processing into fuel rods for its research reactor in Tehran. That would help allay international fears by removing most of the material that Iran could use to make a nuclear weapon.
It would take more than a year for Tehran to replace the enriched material, meaning it would not be able to make a weapon for at least that long.
Iran says it is enriching only to power a future network of nuclear reactors. But because enrichment can also produce fissile warhead material, its program has raised concerns. Iran continues enriching despite three sets of U.N. Security Council sanctions meant to make it freeze that activity and has build an enriched stockpile that could arm two nuclear warheads.
Initially, Tehran appeared to favor the plan. But in recent weeks it has offered modifications that have one thing in common - its refusal to ship out most of its enriched stockpile. That effectively kills the plan, with the West refusing to accept anything else than an Iranian commitment to export the material.
The sextet endorsing the plan - the U.S., Russia, China, Britain, France and Germany - planned to mount a new challenge to Tehran in the form of a resolution at the board meeting criticizing it for ignoring U.N. Security Council and IAEA board demands and continuing to build its enrichment program - sometimes clandestinely.
Impatience with Iran has been fueled by Tehran's September revelation that it had secretly been building a new enrichment facility. In a possible pre-emptive move, Iran notified the IAEA in a confidential letter only days before the leaders of the U.S. Britain and France went public with the project.
Iran says it did not violate IAEA statues by waiting with its notification. But ElBaradei has said Tehran was "outside the law" in not telling his agency about the facility much earlier. On Thursday, he said that Iran's late reporting on the facility reduced "confidence in the absence of other nuclear facilities under construction in Iran which have not been declared to the agency."
A perusal of IAEA records shows that Tehran's chief envoy to the IAEA, Ali Asghar Soltanieh, told the agency's board last year that his country "has repeatedly declared that there is no undeclared nuclear material and activity in Iran" - at the time when construction of the secret nuclear facility was in full force.