VIENNA: Iran could likely build a nuclear bomb in six months or less, a US defence analyst said on Wednesday, but another Western proliferation expert dismissed this as unrealistic.

The differing estimates show the difficulty in trying to assess how long it could take Iran to convert its growing uranium stockpile into weapons-grade material and how advanced it may be in other areas vital for any bid to make a bomb.

Such an assessment could determine the West's room for manoeuvre in trying to find a diplomatic solution to the long-running dispute over Iran's nuclear programme which has the potential to spark a wider conflict in the Middle East.

Laying out one of the shortest potential timelines for Iran to acquire an atomic bomb, Greg Jones of the Washington-based Nonproliferation Policy Education Center (NPEC) said Tehran was moving “ever closer” to such arms.

“If Iran were to now make an all-out effort to acquire nuclear weapons, it could probably do so in two to six months,” Jones wrote in a paper posted on the NPEC's website, which features endorsements by several big name US conservatives.

London-based expert Mark Fitzpatrick said: “This is not realistic. He is basing his assessment on a series of worst-case assumptions, including Iran utilising a method of enrichment that has never been used before for nuclear weapons.”

Iran says its nuclear programme is for peaceful purposes, dismissing allegations of weapons ambitions as based on forged evidence.

A UN nuclear watchdog report last month fuelled concern in the United States, Israel and Europe that Iran is seeking to develop the capabilities needed to make atomic arms.

The report by the International Atomic Energy Agency (IAEA), which said that Iran appeared to have worked on a nuclear weapon design, also stoked speculation that Israel, might launch preemptive strikes against Iranian nuclear sites.

Jones said the report “outlined in unprecedented detail the substantial progress Iran has made in the development of the non-nuclear components needed to produce nuclear weapons”.

ONE BOMB WOULD BE “SUICIDAL”But Iran had no need to make an all-out drive for a nuclear weapon in view of the “ineffectiveness of Western counteraction”, Jones said on the website.

“Rather Iran will probably continue on its current course, producing an ever-growing stockpile of enriched uranium and carrying out additional research to produce non-nuclear weapons components.”

Refined uranium can be used to fuel nuclear power plants, Iran's declared aim, or provide material for bombs if processed much further, which the West suspects is its ultimate intention.

Jones sparked debate in September when he argued that, if Iran decided to make a bomb, it could produce enough highly enriched uranium (HEU) in about eight weeks.

Other analysts said significantly more time would be required, stressing that Iran would need to turn any weapons-usable uranium into the core of a nuclear missile if it wanted more than a crude device, adding to the timetable.

Fitzpatrick said he believed it would take Iran at least “over a year” to make a bomb, adding it was getting closer to this capability but that it would make no sense to produce just one weapon.

“To take the risk of breaking out of the NPT (nuclear Non-Proliferation Treaty) they would want to be able to assemble at least a handful of weapons. Going for one would be suicidal,” said Fitzpatrick, a director of the International Institute forStrategic Studies think tank.

The Arms Control Association, a Washington-based research and advocacy group, said a nuclear-armed Iran was “neither imminent nor inevitable”.

“Sanctions have bought time and helped improve negotiating leverage, but the time available must be used constructively.

Sanctions alone will not turn Tehran around,” it said.