Leaked diagram suggests Iran working on nuclear weapon three times more powerful than Hiroshima bomb

"The application of such studies to anything other than a nuclear explosive is unclear to the agency," the IAEA said at the time.

The models were allegedly created in 2008 and 2009 — well after 2003, the year that the United States said Tehran had suspended such work in any meaningful way. That date has been questioned by Britain, France, Germany and Israel, and the IAEA now believes that — while Iran shut down some of its work back then — other tests and experiments continue today.

With both the IAEA probe and international attempts to engage Iran stalled, there are fears that Israel may opt to strike at Tehran's nuclear program. The Jewish state insists it will not tolerate an Iran armed with nuclear arms.

An intelligence summary provided with the drawing linked it to other alleged nuclear weapons work — significant because it would indicate that Iran is working not on isolated experiments, but rather on a single program aimed at mastering all aspects of nuclear arms development.

The IAEA suspects that Iran has conducted live tests of conventional explosives that could be used to detonate a nuclear weapon at Parchin, a sprawling military base southeast of Tehran. The intelligence summary provided to the AP said data gained from those tests fed the model plotted in the diagram. Iran has repeatedly turned down IAEA requests to visit the site, which the agency fears is undergoing a major cleanup meant to eliminate any traces of such experiments.

The intelligence summary named nuclear scientists Mohsen Fakhrizadeh, Majid Shahriari and Fereidoun Abbasi as key players in developing the computer diagrams, adding that Shahriari and Abbasi were also involved in the Parchin testing.

Iran has for years rebuffed IAEA attempts to question Fakhrizadeh for his suspected involvement in secret programs. Shahriari was assassinated in 2010 by what Iran says were Israeli agents. Abbasi, now the head of Iran's nuclear agency, was wounded in a separate assassination attempt the same day that Shahriari was killed.

The senior diplomat, who is familiar with the Iran probe, said the agency has not yet determined any connection between Parchin and the computer models. But Olli Heinonen, who headed the IAEA's Iran investigation until 2010, said using the results of the alleged Parchin tests would "make sense as part of the design and testing of a (computer) model."