Iran hands over atom bomb blueprint: IAEA

The document -- which Iran said came from a black market offer in 1987 that it never acted upon -- gives "procedural requirements for ... the casting and machining of enriched, natural and depleted uranium metal into hemispherical forms," the International Atomic Energy Agency report said.

Its disclosure raised concerns about Iran's nuclear programme, which Tehran says is a peaceful drive to produce electricity but the United States and Europe fears could be hiding the development of atomic weapons.

Gregory Schulte, US ambassador to the IAEA, told reporters: "Iran owes the (IAEA) board an explanation why it had these documents, what it has done with them, and why it didn't disclose them in the past."

He said the "documents open new concern about weaponisation that Iran has failed to address."