Iran halted its nuclear weapons programme in 2003 and has not restarted it since, a stunning new assessment released yesterday by intelligence agencies in the United States has found.

The findings contradict an assessment by US intelligence officials two years ago that Tehran was seeking nuclear weapons and appear to undercut President Bush’s repeated warnings about Iran becoming a nuclear power.

As recently as August Mr Bush warned that Iran’s pursuit of nuclear technology could lead to a holocaust and that the US “will confront this danger before it is too late”. In October he said that a nuclear-armed Iran could lead to a third world war.

Last night, however, Mr Bush’s closest aides claimed that the finding was vindication for the White House’s muscular but diplomatic approach. Stephen Hadley, Mr Bush’s National Security Advisor, said that the White House was only told last week about the new assessment of Iran’s nuclear programme.

The National Intelligence Estimate (NIE) report — the consensus view of all 16 US intelligence agencies — says that Iran continues to enrich uranium, which means it might be able to develop a nuclear weapon between 2010 and 2015 if it restarts its weapons programme. It also said that Iran’s ultimate goal is still to develop the capability to produce a nuclear weapon.

But it adds: “Tehran’s decision to halt its nuclear weapons programme suggests it is less determined to develop nuclear weapons than we have been judging since 2005.” Two years ago the NIE stated with “high confidence” that Iran was pursuing the nuclear bomb.

Yesterday’s report said that Iran’s ultimate intentions about acquiring a nuclear weapon are unclear, but that Tehran’s decisions “are guided by a cost-benefit approach rather than a rush to a weapon irrespective of the political, economic and military costs.

“Some combination of threats of intensified international scrutiny and pressures, along with opportunities for Iran to achieve its security, prestige, and goals for regional influence in other ways might, if perceived by Iran’s leaders as credible prompt Tehran to extend the current halt to its nuclear weapons programme.”

The assessment comes five years after the release of another report by the NIE which claimed that Iraq possessed chemical and biological weapons and was pursuing the nuclear bomb. The report was one of the main pieces of evidence used by the White House to justify the invasion of Iraq.

It also comes amid a presidential campaign in which the issue of Iran has eclipsed Iraq as the most pressing foreign policy challenge facing the US. Several leading Republican candidates have been bellicose on the issue.

The report addresses claims by President Ahmadinejad of Iran that Tehran has 3,000 centrifuges enriching uranium. It says that Iran might have the centrifuges, but is having difficulties in making them work.

Mr Hadley said: “It [the report] confirms that we were right to be worried about Iran seeking to develop nuclear weapons. The intelligence also tells us that the risk of Iran acquiring a nuclear weapon remains a very serious problem.

“It suggests the President has the right strategy: intensified international pressure along with a willingness to negotiate.”

Last month the International Atomic Energy Agency, the world’s nuclear watchdog, reported that Iran was operating 3,000 uranium-enriching centrifuges. But it said it was unclear if Iran was pursuing a nuclear weapon.

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