“The information indicates that prior to the end of 2003 the activities took place under a structured program; that some continued after 2003; and that some may still be ongoing,” the IAEA said in its latest report on Iran, issued in late August.

Washington still believes that Iran is not on the verge of having a nuclear bomb and that it has not made a decision to pursue one, U.S. officials said in August.

Israel, believed to have the Middle East’s only nuclear arsenal, has threatened military action to stop Iran obtaining such weaponry, although Prime Minister Benjamin Netanyahu last week signaled any attack was not on the cards this year.

In a speech at the annual United Nations General Assembly on Thursday, Netanyahu drew a “red line” on a cartoon bomb just below a label in which Iran was 90 percent along the path to having sufficient weapons-grade material.

Experts put that at the point when Iran has amassed enough uranium, purified to a fissile level of 20 percent, that could quickly be enriched further and be used to produce a bomb.

Iran has produced more than 6.8 tonnes of uranium refined up to 5 percent since 2007, an amount experts say could be used for about five nuclear weapons if processed much further.

Worryingly for the West and Israel, some of that material has been refined to 20 percent, representing most of the effort involved in reaching potential bomb material.

According to the latest IAEA report, Iran has produced about 190 kg of this higher-grade uranium, about half of which has been earmarked for conversion into research reactor fuel, leaving a stockpile in August of just over 90 kg.

Traditionally, about 250 kg is estimated to be needed for a bomb, but some believe less would do.

“It is widely known that even a first device can be made with much less,” the diplomat in Vienna said. But, “no one breaks out to make one warhead. Estimates vary but most think three to five warheads is a minimum to be a real nuclear power.”