Iran has stymied the latest U.N. attempts to probe allegations that it tried to make nuclear arms, dismissing U.S. and other intelligence purportedly proving such efforts as bogus, diplomats told The Associated Press on Tuesday.

The International Atomic Energy Agency — the U.N. nuclear watchdog — will acknowledge its failure to make headway in its efforts to follow up on the allegations in a report to be presented as early as Friday to its 35-nation board, said the diplomats.

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IAEA chief Mohamed ElBaradei was hopeful a month ago in announcing Iran's agreement to review the intelligence collected by the agency, just a few weeks after Tehran declared the books closed on any attempt to look into its alleged nuclear arms programs.

"By the end of May we will be in a position to get the explanation and clarification from Iran" about the allegations, he said back then, describing Tehran's apparent change of heart as a "positive step."

But two diplomats who are familiar with the course of the investigations said that Iran had rejected the evidence presented by agency officials as falsified.

The diplomats, who demanded anonymity because their information is confidential, said Iranian officials insisted during the monthlong probe that all of the nation's nuclear activities — including nearly two decades of clandestine work discovered only six years ago — was peaceful.

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That, said one of the diplomats, amounted to maintaining a disappointing status quo. The Islamic Republic, in rejecting the allegations before agreeing to review the evidence a month ago, had also said any intelligence from the U.S. and other IAEA board nations purporting to prove the contrary was fabricated.

As expected, the report, which will serve as the platform for debate on Iran during the IAEA's June board meeting, will also confirm that Tehran continues to defy three sets of U.N. Security Council sanctions and continues to enrich uranium.

Still, said the diplomats, the confidential report will also note that the enrichment program has not been greatly expanded, despite pronouncements to the contrary by Iranian President Mahmoud Ahmadinejad.

In announcing major progress in Iran's push for nuclear power, Ahmadinejad said last month that his nation's scientists were putting 6,000 new uranium enriching centrifuges into place, about twice the existing number, and testing a new type that works five times faster.
But one of the diplomats said the report will say that the rate of expansion has been much below that touted by Ahmadinejad.

He and other diplomats close to the U.N. nuclear watchdog agency have said Iran has exaggerated its progress and has had problems operating the 3,000 centrifuges already in place. Additionally, the diplomat speculated Tuesday that the Iranian government might be holding back on a quick build-up of its enrichment capabilities because it hopes it can come to terms with the U.S. administration that will succeed President George W. Bush, known for his hard-line Iran policies.

Iran insists its enrichment program is meant only to generate nuclear power. But because of its past clandestine activities, including some that could have applications for weapons research, the international community is concerned that Tehran wants to enrich uranium to weapons grade, suitable for the fissile core of nuclear weapons.

Iran is known to have a little more than 3,000 centrifuges operating at its underground nuclear facility in Natanz. That is the commonly accepted figure for a nuclear enrichment program that is past the experimental stage and can be used as a platform for a full industrial-scale program that could churn out enough enriched material for dozens of nuclear weapons over time.

In the enrichment process, uranium gas is pumped into a series of centrifuges called "cascades." The gas is spun at supersonic speeds to remove impurities. Enriching at a low level produces nuclear fuel, but at a higher level it can produce the material for a warhead.
Iran has said it plans to move toward large-scale uranium enrichment that ultimately will involve 54,000 centrifuges.