Washington believes Tehran working on weapon design despite spy reports that programme has ended

Barack Obama: Reports say his government believes the official intelligence assessment of Iran’s nuclear programme is wrong. Photograph: Alex Brandon/AP

The US believes the official intelligence assessment of Iran‘s nuclear programme is wrong and Tehran is working on the design of a nuclear weapon, it was reported today.

Washington is seeking support for new sanctions against Iran at the UN security council following the expiry of a new year deadline, imposed by the US president, Barack Obama, for Tehran to respond to an offer of economic help and improved diplomatic relations in return for curbing its nuclear programme.

Washington is distancing itself from a controversial National Intelligence Estimate (NIE), produced by several US spy agencies in 2007, which suggested Iran had suspended work on weapons design four years earlier.

“After reviewing new documents that have leaked out of Iran and debriefing defectors lured to the west, Mr Obama’s advisers say they believe the work on weapons design is continuing on a smaller scale – the same assessment reached by Britain, France, Germany and Israel,” the New York Times reported.

The key sources of new intelligence are likely to include two recent Iranian defectors – Ali Reza Asgari, a Revolutionary Guards general who vanished in Istanbul in 2007, and Shahram Amiri, a leading Iranian nuclear scientist, who disappeared while on a pilgrimage to Mecca last summer.

The Iranian government has blamed the US for their disappearance.

However, the Obama administration believes there is still time to try sanctions as a means of stemming Iran’s nuclear ambitions.

It feels there is scope for them to work because of serious technical problems in the country’s uranium enrichment programme and because the regime is distracted by continuing political unrest.

A report by the International Atomic Energy Agency, published late last year, recorded a significant decline in the number of working centrifuges at the enrichment plant in Natanz.

Experts said this could be a result of the technical shortcomings in the Pakistani centrifuge design Iran bought from the rogue nuclear scientist Abdul Qadeer Khan and also because of a covert sabotage campaign by the west.

Iran – which denies having any ambitions to acquire nuclear weapons – currently has enough low enriched uranium to make a single bomb if it was further enriched to weapons grade purity.

Western officials have said it would take more than a year for the Tehran to accumulate enough for even a small arsenal.

“For now, the Iranians don’t have a credible breakout option, and we don’t think they will have one for at least 18 months, maybe two or three years,” a senior Obama administration official told the New York Times.

The newspaper also quoted a senior Israeli diplomat in Washington as saying that Israel was prepared to put military options on hold for the time being.

“Obama has convinced us that it’s worth trying the sanctions, at least for a few months,” the diplomat said.