Iran experts at the United Nations' nuclear monitoring agency believe Tehran has the ability to make a nuclear bomb and worked on developing a missile system that can carry an atomic warhead.
A confidential report, seen by the Associated Press and drafted by senior officials at the International Atomic Energy Agency (IAEA), gives the clearest indication yet that those officials share the US government's views on Iran's weapon-making capabilities and missile technology - even if they have not made those views public.
The document, titled Possible Military Dimension of Iran's Nuclear Program, appeared to be the so-called IAEA "secret annex" on Iran's alleged nuclear arms program that the US, France, Israel and other IAEA members say is being withheld by agency chief Mohamed ElBaradei - claims which the nuclear watchdog denies.
It is a record of IAEA findings since the agency began probing Iran's nuclear program in 2007 and has been continuously updated.
The information in the document that is either new, more detailed or represents a more forthright conclusion than found in published IAEA reports includes:
- The IAEA's assessment that Iran worked on developing a chamber inside a ballistic missile capable of housing a warhead payload "that is quite likely to be nuclear".
- That Iran engaged in "probable testing" of explosives commonly used to detonate a nuclear warhead - a method known as a "full-scale hemispherical explosively driven shock system".
- An assessment that Iran worked on developing a system "for initiating a hemispherical high explosive charge" of the kind used to help spark a nuclear blast.
- In another key finding, an excerpt notes: "The agency ... assesses that Iran has sufficient information to be able to design and produce a workable implosion nuclear device (an atomic bomb) based on HEU (highly enriched uranium) as the fission fuel."
Mr ElBaradei said in 2007 there was no "concrete evidence" that Iran was engaged in atomic weapons work - a source of friction with the US, which has sought a hard-line stance on Tehran's nuclear ambitions.
Responding to the AP report, the agency did not deny the existence of a confidential record of its knowledge and assessment of Iran's alleged attempts to make nuclear weapons. But an agency statement said the IAEA "has no concrete proof that there is or has been a nuclear weapon program in Iran".
It cited Mr ElBaradei as telling the agency's 35-nation governing board last week that "continuing allegations that the IAEA was withholding information on Iran are politically motivated and totally baseless".
"Information from a variety of sources ... is critically assessed by a team of experts working collectively in accordance with the agency's practices," it said.
"The IAEA reiterates that all relevant information and assessments that have gone through the above process have already been provided to the IAEA board of governors in reports of the director general."
Meanwhile, Iranian President Mahmoud Ahmadinejad, refused to rule out ever building nuclear weapons, but said repeatedly that he saw "no need" for them.
"Nuclear arms, we believe, belong to the past and the past generation," he said.
The IAEA document traces Iran's nuclear arms ambitions as far back as 1984, when current supreme leader Ayatollah Ali Khamenei was president and Iran was at war with Iraq.
At a top-level meeting at that time, according to the document, Mr Khamenei endorsed a nuclear weapons program, saying "a nuclear arsenal would serve Iran as a deterrent in the hands of God's soldiers".
He and other top Iranian leaders insist their country is opposed to nuclear weapons, describing them as contrary to Islam. They argue that Iran's uranium enrichment program and other activities are strictly for civilian purposes.
Iran is under three sets of UN Security Council sanctions for refusing to freeze enrichment, the key to making both nuclear fuel and weapons-grade uranium.