The United States said today Iran was nearing the ability to make atom bombs by stockpiling enriched uranium and, with EU allies, prodded Tehran to engage in talks now on its nuclear ambitions.
Western powers spoke at a UN nuclear watchdog meeting in Vienna as Iran's state television announced that it would hand over a long-delayed package of proposals for talks "very soon" amid Western talk of pursuing far harsher sanctions against Tehran.
"We have serious concerns that Iran is deliberately attempting, at a minimum, to preserve a nuclear weapons option," US envoy Glyn Davies told the 35 countries on the International Atomic Energy Agency's Board of Governors.
"Iran is now either very near or in possession already of sufficient low-enriched uranium to produce one nuclear weapon if the decision were made to further enrich it to weapons-grade ... (This) moves Iran closer to a dangerous and destabilising possible breakout capacity," Mr Davies said.
IAEA Director-General Mohamed ElBaradei replied that his non-proliferation inspectors had "serious concerns" about Iran's nuclear intentions, but the organisation was not in a state of panic.
"That is because we have not seen diversion of nuclear material (from declared civilian uses), we have not seen components of nuclear weapons. We do not have any information to that effect," he said.
Mr ElBaradei was effectively shooting down Israeli and French suggestions the IAEA was withholding stronger evidence of a covert Iranian nuclear weapons drive parallel to its declared programme of enriching uranium for electricity generation.
But he said intelligence material suggesting Iran had illicitly studied how to assemble nuclear arms was serious and Tehran must address it, not just issue unsubstantiated denials.
"If this information is real, there is a high probability that nuclear weaponisation activities took place (in Iran)."
US national intelligence director Dennis Blair estimated earlier this year that Iran probably would be unable technically to "weaponise" enrichment before 2013.
Mr Davies' remark pointed to growing Western disquiet about Iran's nuclear advances, largely out of sight due to restrictions on UN inspections.
An IAEA report last month said Iran had somewhat improved transparency by approving tighter monitoring of its Natanz enrichment plant and allowing inspectors to revisit a reactor site of proliferation concern after a year-long ban on access.
Iran had also slightly reduced, as of mid-August, its number of centrifuge machines refining uranium, the report said, a move diplomats said pointed to repair and maintenance work.
But the IAEA also said Iran had raised its total number of installed centrifuges by 1,000 to 8,300, expanding potential enrichment capacity, and was still blocking an IAEA inquiry into allegations it has tried to "weaponise" the enrichment process.
Iran has said its package for world powers addresses global "challenges" but also reaffirmed an unwillingness to negotiate on its campaign to enrich uranium, a process Western powers suspect Iran will eventually put to making atom bombs. Iran says it seeks only electricity from enrichment.
Britain, France and Germany, among the six powers dealing with Iran, said its "persistent defiance and point-blank refusal" to halt enrichment and avoidance of talks demanded by UN Security Council resolutions, was unacceptable.
President Barack Obama has indicated Iran will face much harsher US sanctions targeting its vital oil sectorif it does not accept negotiations by the end of September.