The U.S. envoy to the International Atomic Energy Agency says the latest information on Iran's nuclear ambitions shows that there are clear indications of a weapons' program. The ambassador, Gregory Schulte, spoke to reporters before the upcoming IAEA executive meeting.

A confidential report prepared by the IAEA for a board meeting starting Thursday shows that Iran obtained detailed instructions related to nuclear technology that would have no place in a program used for civilian purposes.

Diplomats close to the IAEA say the instructions - which reportedly show how to cast enriched, natural and uranium metal into so-called hemispherical forms - could indicate a design for the core of a nuclear warhead. Gregory Schulte, U.S ambassador to the IAEA, says many countries are worried by this revelation.

"The most disturbing bit of information reported to us was the fact that the inspectors had uncovered this document that describes how to machine uranium into a hemisphere and to our knowledge about the only real reason to machine uranium into a hemisphere is to produce nuclear weapons," he said.

Iran has told the IAEA that it never asked for the designs on how to shape the uranium metal, and that the information was passed along by the black market nuclear network run by disgraced Pakistani scientist AQ Khan. Tehran insists its nuclear program is for peaceful purposes only.

In the past the IAEA has found so-called "dual purpose technology" in Iran which could be used for weapons or for producing electricity.

But Mr. Schulte says this time the IAEA report raises many questions about the potential for so-called weaponization of Iran's nuclear program.

A senior State Department official, who did not want to be named, said the fact that Iran wants to carry out enrichment activities on its soil is a further indicator that Tehran is working on a nuclear weapons breakout capability.

The United States is hoping that the IAEA board, at its meeting on Thursday, will agree to keep up the pressure on Iran to come out of its isolation and return to negotiations with the European Union and Russia.