VIENNA, Austria — The U.N. nuclear monitoring agency on Wednesday announced what it called a "milestone" agreement with Iran that aims to provide answers about allegations that Tehran tried to develop nuclear weapons.

International Atomic Energy Agency chief Mohamed ElBaradei said IAEA Deputy Director General Olli Heinonen and his team had agreed with Iran to start a process aiming to clarify the issue in May.

"That is certainly a milestone and hopefully by the end of May we will be in a position to get the explanation and clarification from Iran as to these alleged studies," ElBaradei said in Sarajevo before collecting an award from a Bosnian university. "This, in my view, is a positive step."

ElBaradei called the issue "the only remaining topic for us to investigate about past and present Iran nuclear activities" — a statement likely to be challenged by the U.S. and other nations suspicious that Tehran may be hiding an undeclared nuclear program.

Tehran has denied ever trying to make nuclear weapons and has rejected the evidence as fake. But U.S. intelligence agencies say Tehran experimented with such programs until 2003 and other countries believe it continued past that date.

Iran is under three sets of U.N. Security Council sanctions for its refusal to suspend uranium enrichment and meet other council demands designed to ease fears its civilian nuclear program is a cover for attempts to make atomic arms.

Any agreement by Iran to at least further discuss the allegations is a positive sign.

Last Sunday, Gholam Reza Aghazadeh, the head of Iran's nuclear program, abruptly canceled a meeting with ElBaradei. The meeting had been considered a test of whether Iran will continue to stonewall the Vienna-based agency in its attempt to investigate the alleged military programs.

Intelligence received by the IAEA from the U.S. and other agency board member nations and the agency's own investigations suggest that Iran experimented with an undeclared uranium enrichment program that was linked to a missile project and drew up blueprints on refitting missiles to allow them to carry nuclear warheads.

The intelligence also suggested Iran was researching construction of an underground site that apparently could be used for test nuclear explosions and ordered "dual use" equipment from abroad that could be part of a nuclear weapons program.

Additionally, Iran possesses diagrams showing how to mold uranium metal into the shape of warheads.

While the Islamic Republic says its enrichment program is meant to generate nuclear fuel, its past nuclear secrecy and defiance of the Security Council are fueling fears it could decide to use the technology to make the weapons-grade enriched uranium used for the fissile core of nuclear arms.

In Iran on Wednesday, President Mahmoud Ahmadinejad warned that those imposing pressure on Iran on enrichment will suffer even as he said that his country remained prepared to discuss its nuclear activities with the outside world.

"The enemies should know that the Iranian nation is for logic and dialogue with any of you if the criteria is justice and respect," Ahmadinejad told thousands of Iranians in western Iran. "But if you resort to deception and seek to impose (your demands), ... the Iranian nation will heavily slap bad-wishers in the mouth."


Associated Press writers Aida Cerkez-Robinson in Sarajevo, Bosnia-Herzegovina, and Ali Akbar Dareini in Tehran, Iran, contributed to this report.