A meeting between a senior Iranian envoy and the head of the International Atomic Energy Agency was abruptly canceled Monday and diplomats blamed Iran's refusal to make good on a promise to provide answers about past atomic activities.

The meeting, between Javeed Vaidi of Iran and IAEA director general Mohamed ElBaradei, had been billed as a test of Tehran's readiness to end years of stonewalling and provide answers on aspects of its nuclear program that could be used to develop weapons.

But the talks were canceled on short notice because of perceptions that Vaidi would bring "nothing substantial" to another meeting with deputy IAEA director general Olli Heinonen, a diplomat told The Associated Press.

Along with Tehran's refusal to freeze uranium enrichment and restrictions on IAEA inspectors, Iranian stonewalling was also the focus of ElBaradei, in opening comments to a meeting of the agency's 35-nation board of governors.

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The agency is unable "to make any progress in its efforts to resolve outstanding issues relevant to the nature and scope of Iran's nuclear program," ElBaradei told delegates, describing the development as a "key proliferation concern."

"Against the background of many years of undeclared activities, and taking into account the sensitivity of nuclear enrichment technology, it is incumbent on Iran to work urgently with the agency ... in order for the agency to be able to provide assurance regarding the exclusively peaceful nature of all of Iran's nuclear activities," ElBaradei said.

Vaidi did talk with EU negotiator Robert Cooper to discuss a recent Iranian pledge to clear up past nuclear questions in talks at Austria's foreign ministry. Still, the cancellation of subsequent meetings — first with ElBaradei and then with Olli Heinonen, a key ElBaradei aide — dashed hopes that the Iran was prepared for a breakthrough compromise on one of the issues that led to its referral last year to the U.N. Security Council.

It was also likely to give support to Iran critics at the board meeting, with the United States and its allies using that gathering as a platform to pressure Tehran on enrichment and other issues.

Gregory L. Schulte, the chief U.S. delegate to the gathering, set the tone for countries pushing Iran.

"Iran's leaders [are] continuing to develop capabilities to enrich uranium and produce plutonium" in violation of the Security Council, Schulte told reporters. "These capabilities are not necessary to benefit peaceful nuclear technology but are necessary to produce fissile material for nuclear weapons."

He took Tehran to task for "continuing to withdraw cooperation from the IAEA, causing a troubling deterioration of the agency's knowledge of Iran's nuclear capabilities."

The Vaidi-Cooper talks are a spinoff of May 31 discussions in Madrid between EU foreign policy chief Javier Solana and Ali Larijani, Iran's top nuclear negotiator.

That meeting ended with Iran offering to divulge information long sought by IAEA experts trying to establish whether Tehran's past nuclear activists were secretly aimed at trying to make weapons.

The offer fell short of the main purpose of the Solana-Larijani talks — finding a way to bridge an impasse over Iran's rejection of U.N. Security Council demands that it suspend uranium enrichment.

Still, any decision by Iran to fully cooperate on clearing up past activities would have represented a major concession — a hope diminished with news that the Vaidi-ElBaradei meeting had been canceled.

An IAEA report two weeks ago provided the potential trigger for new U.N. sanctions, saying Iran continued to defy the Security Council and was instead expanding its enrichment activities.

The report was also critical of Iran's refusal to answer questions about nearly two decades of clandestine nuclear activities that first came to light four years ago.

The concerns include: traces of enriched uranium at a facility linked to the military, which could be a sign of a weapons program; lack of documentation on Iran's past enrichment activities, and possession of documents showing how to form uranium metal into the form of missile warheads.

Iran insists its enrichment program is only for meeting future power needs and argues it is entitled to pursue the technology under the Nuclear Nonproliferation Treaty. But suspicions the program could be used to produce fissionable material for weapons have led to U.N. sanctions.

With disagreements within the Security Council over what kind of new sanctions should be imposed and how quickly, diplomats said the United States was looking to play up new evidence of Iranian nuclear defiance at the IAEA board meeting. The diplomats, who were all involved in international attempts to persuade Iran to give up enrichment, demanded anonymity because their information was confidential.

Such evidence could include Iran's decision earlier this year to annul part of an agreement linked to the Nonproliferation Treaty under which the country is obligated to report promptly any decision to build a new nuclear facility or expand an existing one.

The diplomats said the Americans failed to get support for an IAEA board resolution stating that Iran was in noncompliance with its NPT obligations for its refusal to allow agency inspections of its Arak heavy water reactor. The reactor, once completed sometime in the next decade, will produce plutonium, like enriched uranium a possible pathway to nuclear arms. But they said the U.S. would continue to press its case in hopes of raising Security Council sentiment for new sanctions.

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