An exiled Iranian opposition group said on Saturday that Iran has some 60 scientists and engineers involved in a concerted and expanding program to develop nuclear weapons under defense ministry auspices.

However, diplomats say the National Council of Resistance of Iran has had a spotty record with allegations about Iran’s nuclear work since exposing a secret uranium enrichment plant at Natanz in 2002. A top US nuclear expert said the NCRI report, like previous ones, should be treated with great skepticism.

Its latest report, whose details could not be verified, appeared timed to encourage a tougher line at talks with Iran the UN nuclear watchdog will have in Vienna on Monday and Tuesday and six world powers will hold in Baghdad on May 23.

But it clashed with the assessment of US and Israeli intelligence officials that Iran has not decided whether to “weaponise” its enrichment program. Tehran says it is refining uranium solely for peaceful energy.

In the six-page report shown to Reuters, the Paris-based NCRI cited sources in Iran’s government and military as saying some 60 scientists were pursuing bomb-relevant research in 11 agencies operating clandestinely under defense ministry control.

“Information ... shows that the clerical regime has expanded the organization responsible for nuclear weapons development,” the report said. “This finding reveals a complete and elaborate, and highly ... secret research structure and a network for procurement of the required parts and equipment.

“So far, the identities of 60 directors and experts working in various parts of the New Defense Research Organization and 11 institutions and companies affiliated with it have been detailed,” the report went on.

It featured diagrams said to lay out the disguised command structure and named scientists and engineers involved.

The NCRI, an umbrella bloc of five opposition groups in exile that seek an end to Shiite Muslim clerical rule in Iran, urged the International Atomic Energy Agency to launch a “robust probe” into Iran’s nuclear program and all personnel involved.

Iran says it is stockpiling enriched uranium for a future network of nuclear power plants. But the world’s No. 5 oil exporter has stonewalled an almost decade-old IAEA investigation into suspected military dimensions to its atomic activity.

World powers trying to rein in Iran’s nuclear activity via negotiations want to halt a spiral toward confrontation that has stoked fear of a new Middle East war, with Israel mooting last-resort air strikes on the nuclear sites of its arch-enemy.

But Western leaders have rejected Iranian calls for an end to UN sanctions against it as a precondition for any deal.

No 'smoking gun'

In its last quarterly report on Iran issued in February, the IAEA cited generally credible information indicating Iran had carried out activities relevant to developing a nuclear explosive, but without evidence of actual weaponization.

The NCRI is the political wing of the People’s Mujahideen Organization of Iran (PMOI), which the United States classifies as a terrorist organization.

David Albright, head of an influential Washington-based think tank that tracks Iran’s nuclear work and has access to sensitive intelligence, said “we have to be extremely skeptical of whatever they (the NCRI) say.

“(They are) an activist group with a huge incentive to say there is a nuclear weapons program that is making great progress, ” Albright said when asked about the report.

“We know this organization exists,” he said, referring to the command structure cited by the NCRI. “We know the (NCRI) receives intelligence information from countries so sometimes it is good, but the trouble is, they fill in details ...(without) evidence. You just don’t know whether it’s true or not.”

Albright said the best available evidence was that Iran “doesn’t have a structured, coherent, active nuclear weapons program ... Most of their effort is really focused on developing the capability to make nuclear explosive material...

“The real bottleneck in their program is the lack of any ability to make weapons-grade uranium quickly.”

Refined uranium can be used to fuel nuclear power plants, which is Iran’s stated aim, or provide the core for a bomb if enriched to a much higher degree of fissile purity.

EU foreign policy chief Catherine Ashton referred without qualification to Iran’s “nuclear weapons program” on Friday. But her language went beyond that of Western security officials who are more plugged in to Iran’s activities, describing them as an attempt to advance toward a nuclear weapons capability.

In January, US intelligence chief James Clapper said Iran was keeping the option open to develop a bomb but US intelligence agencies did not know whether it would eventually decide to build one.

At the Vienna talks next week, the IAEA will once again try to get Iran to address suspicions about military aspects to its nuclear work. Atop the IAEA’s agenda will be gaining access to a military site that they fear Iran may be “sanitising” to remove incriminating evidence of tests relevant to nuclear weapons.

The following week, the six big powers - the United States, Russia, China, Britain, France and Germany - will seek gestures from Iran that would evolve into guarantees that it is not after atomic bombs. These could include much more intrusive IAEA inspections and limits on Iranian capacity to refine uranium.