A UN nuclear watchdog report says there are "serious concerns" about Iran's nuclear activites, and "credible" information Tehran may have worked on developing atomic weapons.
"The agency has serious concerns regarding possible military dimensions to Iran's nuclear programme," the keenly awaited International Atomic Energy Agency report said, saying its information is "overall, credible."
"This information indicates that Iran has carried out activities relevant to the development of a nuclear explosive device," calling on Tehran to "engage substantively with the agency without delay."
The document, which has been preceded by Israeli media speculation of military strikes against Iranian nuclear sites, detailed new evidence suggesting efforts to develop a nuclear arms capability.
Some of the activities may still be going on, it said.
The United States and its allies are expected to seize on the keenly-awaited IAEA report to press for more sanctions on the major oil producer.
Tehran has dismissed the allegations as fabricated and baseless.
Israeli minister plays down Iran attack rumours
Meanwhile Defence Minister Ehud Barak has played down speculation that Israel intended to strike Iranian nuclear facilities, saying it had not decided to embark on any military operation.
"War is not a picnic. We want a picnic. We don't want a war," Barak told Israel Radio.
"(Israel) had not yet decided to embark on any operation," he said, dismissing as "delusional" Israeli media speculation that he and Prime Minister Benjamin Netanyahu had chosen that course.
But he said Israel had to prepare for "uncomfortable situations" and ultimately bore responsibility for its own security.
All options to curb Tehran's nuclear ambitions should remain open, Barak said, repeating the official line taken by Israel, which has termed a nuclear-armed Iran a threat to its existence.
Ahmad Vahidi, Iran's defence minister, cautioned against any military strike against its atomic facilities.
"We are fully prepared for a firm response to such foolish measures by our enemies," Vahidi was quoted as saying by Iran's students' news agency.
