But they said it was unclear whether the International Atomic Energy Agency (IAEA) would go as far as to make a firm assessment on whether it believes Iran is working to develop a nuclear missile, as Tehran’s Western foes want the agency to.

The diplomats voiced skepticism about an article in France’s Le Figaro paper, which said the IAEA was preparing to denounce “the military nature of this program aimed at providing Iran with the bomb”. Figaro did not name its sources.

Any conclusion by the UN agency, in a quarterly inspection report on Iran due early next month, giving independent backing to Western fears about Iran’s aims could strengthen the US case for further punitive measures against Tehran.

French Foreign Ministry spokesman Bernard Valero said in Paris: “This (IAEA) report has not been communicated yet … and as far as we know there is still some way to go before it is being finalized.”

US President Barack Obama warned Iran on Thursday it would face the toughest possible sanctions for an alleged plot to kill the Saudi ambassador in Washington, as Treasury officials eyed action against the Iranian central bank.

Iran has dismissed the plot accusations as a fabrication designed to stir tensions in its ties with its Arab neighbors.

It also rejects Western allegations that its nuclear program is a disguised bid to develop nuclear arms capability.

But the report by the IAEA, tasked with preventing the spread of nuclear arms in the world, is expected to spell out in greater detail the reasons why it said last month it is “increasingly concerned” about Iran’s nuclear program.

The document is being drafted by agency experts ahead of a Nov. 17-18 meeting of the IAEA’s 35-nation governing board, which has the power to report states to the UN Security Council if they violate non-proliferation rules.

The United States and its allies have urged IAEA Director General Yukiya Amano to declare plainly whether he believes that there are military aspects to Tehran’s nuclear activities.

“The indications right now are that it will be a very strong report offering a good amount of detail on possible military dimensions,” one Western diplomat said.

IAEA ‘on the horns of a dilemma’

Another envoy painted a similar picture, saying he expected the IAEA to make a fuller analysis on the basis of the information it has at its disposal about possible military aspects to its nuclear activities.

The IAEA has said in previous reports that the data it has received about such issues is extensive and comprehensive, and also “broadly consistent and credible” in terms of technical detail and the time frame.

But diplomats and analysts expressed doubt that Amano would make a conclusion regarding Iran as clear-cut as one about Syria in a report in May, when he said a facility bombed by Israel in 2007 was “very likely” to have been a secret nuclear reactor.

“To come to a Syria-type conclusion is going to be difficult,” one nuclear proliferation expert said.

For several years the IAEA has been investigating Western intelligence reports indicating Iran has melded efforts to process uranium, test explosives at high altitude and revamp a ballistic missile cone to accommodate a nuclear warhead.

Iran, the world’s No. 5 oil producer, says those allegations are forged and that it enriches uranium, activity that can have both civilian and military purposes, solely as an alternative source of electricity for a growing population.

But its history of concealing sensitive nuclear activity and its refusal to suspend work that also can also yield atomic bombs have drawn four rounds of UN sanctions, as well as separate US and European punitive steps.

Ali Vaez of the Federation of American Scientists, a Washington-based think tank, said he believed Amano has found himself “on the horns of a dilemma” in preparing his report.

“If he publishes classified documents of a member state, in the absence of a smoking gun, he could undermine the agency’s credibility,” Vaez said.

“If he simply lists a few issues of concern without hard evidence, Iran could reject the allegations out of hand and further reduce its cooperation with the agency.”