Joe Cirincione, global security analyst at the Center for American Progress, said the powers needed to proceed cautiously since no hard proof of atom bombmaking has been found by IAEA investigators in Iran, although many questions persist.

"Most of the evidence points to a program to slowly develop the capability for producing nuclear weapons some time in the future should Iran decide to do so," Cirincione said.

Iran says it is pursuing a peaceful program permitted by the nuclear Non-Proliferation Treaty to generate energy and has denounced pressure for an unconditional suspension as illegal.

"Enrichment is clearly the prize of negotiations and Iran clearly does not want to give it up before talks happen," said Trita Parsi, a U.S.-based Iranian author and specialist.

But concerns about Iran's intentions have been fanned by its record of hiding sensitive nuclear work from the IAEA for 18 years, failure to cooperate fully with agency probes and calls for Israel's destruction, Western officials say.

Probe targets since 2003 include plutonium experiments, alleged administrative links between processing of uranium ore, explosives tests and a missile warhead design, and black-market acquisitions of parts for centrifuge enrichment machines.

ElBaradei's report may state that Iran has stonewalled the myriad inquiries to a standstill, one senior diplomat said.

Iran is withholding answers to IAEA questions as bargaining chips for crunch talks with the big powers, diplomats say.

Analysts believe Iran remains 3-10 years away from producing highly-enriched uranium needed for a bomb, assuming it wants to.

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