The United States and its European allies are preparing a new offer to Iran on a possible nuclear fuel swap that would include tougher conditions than those rejected by Tehran last year, the New York Times said.
Western diplomats told Reuters that even if the fuel exchange plan was revived during talks they hope will get under way in Vienna next month, it would not resolve wider concerns about Iran's nuclear intentions.
It "could be a useful way of building confidence ... but it is not in itself a solution to the problem," one envoy said.
The New York Times cited a senior U.S. official as saying the Obama administration and its partners were "very close to having an agreement" on a position to present to Tehran.
But it added that intelligence analysts had concluded that last year's fuel exchange proposal was scuttled by Iran's supreme leader, Ayatollah Ali Khamenei, and that many officials therefore suspected that this latest effort would also fail.
"I for one am sceptical that the Iranians will change course ... what comes out of Iran is not very promising," another senior diplomat told Reuters in Vienna.
Iran, which has ruled out halting sensitive nuclear work which can have both civilian and military uses, has welcomed the offer of talks with the major powers but has yet to formally reply to the invitation for a meeting from Nov. 15 to 17.
Dismissing the impact of tougher sanctions introduced since June, it has said it is open to resume negotiations on a proposal for it to send low-enriched uranium (LEU) abroad and get higher-grade fuel for a medical research reactor in return.
Western diplomats say it is possible to try and revive the fuel swap plan if Iran also accepts broader talks which they hope will lead to Tehran agreeing to curb its enrichment drive.
They have made clear that any new swap deal must be updated to take into account Iran's increased uranium stockpile and its work to enrich to higher levels since February.
The Times said the new offer would require Iran to send more than 4,400 pounds (2,000 kg) of LEU out of the country. That would represent a more than two-thirds' increase from the amount required under a tentative deal a year ago that later collapsed.
It said the increase reflected Iran's steady production of uranium over the past year and Washington's goal to ensure Iran has less than a bomb's worth of uranium on hand.
Iran would also be required to stop all production of nuclear fuel it is enriching to 20 percent, a key step toward bomb-grade levels, and agree to negotiate on the future of its nuclear programme.
Research Associate Ivanka Barzashka of the Washington-based Federation of American Scientists said a successful fuel deal was a necessary condition for further Iran-West engagement and that its confidence-building benefits could still be salvaged.
But, "an increase in the swap amount will surely be seen by Iran as moving goalposts and will likely cause further delays in negotiations," Barzashka said in an e-mailed comment.
© 2015 Thomson/Reuters. All rights reserved.