The U.N. nuclear agency on Thursday denied Iran technical help in building a plutonium-producing reactor but left room for Tehran to eventually renew its request, diplomats said. A defiant Iran said it would press ahead with the project.

The 35-nation governing board of the International Atomic Energy Agency waived a decision on Tehran's request for aid for its Arak reactor. That, in effect, denied Iran IAEA help on Arak for at least the next two years. The project may be resubmitted after that time has passed.

Iran says it needs Arak for the production of radioactive isotopes for diagnosing and treating cancer, and wanted agency assistance to ensure the reactor is environmentally safe.

But the plutonium the Arak facility would produce could give Iran a second possible path to a nuclear weapon — enough plutonium for about two bombs a year. Most international efforts have focused on Tehran's efforts to enrich uranium.

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Iranian Foreign Minister Manouchehr Mottaki said the IAEA was legally required to provide technical assistance to Iran, a signatory to the Nuclear Nonproliferation Treaty. Iran has repeatedly said its contentious nuclear program is for peaceful purposes only.

"It is the duty of the IAEA to help. If they help, we will appreciate it," Mottaki told reporters in Tehran. "If not, we will do it on our own."

A text accepted by the IAEA board in a consensus decision said that all requests for IAEA technical aid submitted by member countries were approved "with the exception of" Arak, said a senior diplomat who was in the closed meeting.

That formulation allowed countries from opposite sides of the issue to claim victory, with the United States and its allies saying it constituted denial, and developing countries who traditionally support Iran interpreting it as deferral.

Gregory L. Schulte, the chief U.S. delegate to the IAEA, said Arak was "removed entirely from the program, not just deferred," adding: "Never has Iran been so isolated."

The U.S. and the IAEA are not prepared to help countries build nuclear bombs," he told reporters.

The full board also reviewed a report on the latest stage of a nearly four-year IAEA investigation into Iran's nuclear activities.

That report essentially says that the agency has been unable to make headway in determining whether suspicions that Tehran is interested in making nuclear weapons are well-founded.

IAEA chief Mohamed ElBaradei said his inspectors had "not been able to make any progress" in their investigation.

"This is essentially due to the decision by Iran to limit its cooperation," he said. "The IAEA is therefore unable to move forward in its efforts to confirm the absence of undeclared nuclear material and activities in Iran. This, naturally continues to be a matter of serious concern."

Technical aid requests for projects like Arak are normally approved without discussion. Developing countries — the key recipients of IAEA technical help — are worried that denial of aid for any project would set a precedent that would hurt their future chances of getting agency support.

Arak is one of seven or eight projects submitted by Iran — lists circulated at the meeting have conflicting numbers. Most, if not all, of the 35 nations had no trouble with approving Iran's request for help with the other far less contentious projects, said the diplomats.

Rebuffing Iran's Arak request would not affect its construction and would also have no effect on the country's other potential avenue to weapons production — uranium enrichment.

Still, it would maintain at least symbolic pressure while the U.N. Security Council is deadlocked over how to sanction Iran for ignoring demands to stop enriching uranium.