By Adam Brookes
BBC News, Washington
In an abrupt change of position, the US intelligence agencies now say they do not know if Iran intends to build a nuclear weapon.
The report says Iran may still face problems enriching uranium
The unclassified version of a new National Intelligence Estimate, or NIE, released on Monday, said that Iran was "less determined to develop nuclear weapons than we have been judging since 2005".
In May 2005, the intelligence community had said "with high confidence" that Iran was "determined" to build nuclear weapons.
The new NIE confirms that Iran did, indeed, have an illicit nuclear weapons programme.
But it says that programme ceased operating in 2003 and, as of mid-2007, had probably not started up again. The NIE asserts that the weapons programme was dropped because of international pressure.
It says that US intelligence estimates - with "moderate-to-high confidence" - that Iran currently does not currently have a nuclear weapon.
The NIE affirms, however, that Iran continues its efforts to enrich uranium.
The document estimates that the very earliest Iran could produce enough highly-enriched uranium (HEU) for a weapon would be late 2009, but some time between 2010 and 2015 is more likely.
In an interesting note of dissent, the state department's Bureau of Intelligence and Research does not think enough HEU for a weapon could be produced until 2013.
In all, the new NIE argues that Iran's intentions may be less threatening than US intelligence previously thought.
And it strongly suggests large gaps in the Americans' knowledge of exactly what the Iranian programme is capable of.
But the document emphasises that Iran continues to build a capacity which could be turned to nuclear weapons production in the future.
"Iranian entities are continuing to build a range of technical capabilities that could be applied to producing nuclear weapons, if a decision is made to do so," it reads.
Iran continues to insist that its programme is for civilian purposes.
The Bush administration welcomed the NIE, even though it might be seen to contradict the administration's warnings about the gravity of the Iranian threat.
The National Security Adviser, Stephen Hadley, said the report showed that the risk of Iran's acquiring a nuclear weapon remained a "very serious problem".
Mr Hadley said that the NIE showed that the US had the "right strategy" in pressuring Iran to suspend its entire nuclear programme, while offering to negotiate.
His statements suggest that the new NIE will not engender any profound shift in policy on the part of the Bush administration, and that Washington will continue to push for a new round of UN sanctions against Iran.
But Washington analysts were predicting that the intelligence community's new position would complicate the effort to bring about a new UN Security Council Resolution imposing sanctions.
Such a resolution was still within reach, they said, simply because Iran has not complied with demands to suspend uranium enrichment.
But, they said, the US will be hard put to maintain a sense of urgency following the release of the new NIE.
However, the new NIE will make it harder for proponents of military action against Iran to argue their case.
One source, who has close links to US intelligence, said that members of Vice President Dick Cheney's staff continued to call for military strikes against Iran "on a daily basis".
Senior military officers and intelligence officials are understood to have grave reservations about an attack on Iran - not least because it would be unclear how a military confrontation with Iran could be brought to a conclusion.