The International Atomic Energy Agency document, which has been preceded by Israeli media speculation of military strikes against Iranian nuclear sites, detailed new evidence suggesting efforts to acquire a nuclear arms capability.
"The agency has serious concerns regarding possible military dimensions to Iran's nuclear programme," the IAEA said in the report, obtained by Reuters.
Citing "credible" information, the Vienna-based agency said the data "indicates that Iran has carried out activities relevant to the development of a nuclear explosive device." It added: "The information also indicates that prior to the end of 2003, these activities took place under a structured programme, and that some activities may still be ongoing."
The US and its allies are expected to seize on the report to press for more punitive sanctions on Iran over its record of hiding sensitive nuclear activity and lack of full cooperation with UN inspectors.
Teheran has dismissed the allegations of covert atomic bomb research as fabricated.
- French President Nicolas Sarkozy branded Israeli Prime Minister Benjamin Netanyahu "a liar" in a private conversation with US President Barack Obama that was accidentally broadcast to journalists during last week's G20 summit in Cannes.
"I cannot bear Netanyahu, he's a liar," Sarkozy told Obama, unaware that the microphones in their meeting room had been switched on, enabling reporters in a separate location to listen in to a simultaneous translation.
"You're fed-up with him, but I have to deal with him even more often than you," Obama replied, according to the French interpreter.
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