Destroying the Bush administration's main rationale for war against Iraq, the chief US weapons inspector declared yesterday that Saddam Hussein had neither weapons of mass destruction nor programmes to manufacture them at short notice when the US and its allies invaded in March 2003.
Charles Duelfer told the Senate Armed Services Committee he did not believe that "militarily significant" WMD stockpiles were hidden in Iraq.
He also said that Iraq's nuclear programme was nothing compared to what it had been in 1991, at the time of the previous invasion and amounted to less even than in 1998, when the United Nations weapons inspectors were withdrawn.
Tony Blair sought to minimise the damning conclusion of the report, saying: "This case is a far more complicated situation than many people thought.
"Just as I accept that the evidence now is that there were no stockpiles of actual weapons ready to be deployed, others can be honest and accept that the report also shows that sanctions were not working.
"On the contrary, Saddam Hussein was doing the best to get around those sanctions, with every intention of developing those programmes of weapons of mass destruction ... and there were multiple breaches of the United Nations resolutions, which were the legal justification for the conflict."
The report states that the Iraq Survey Group (ISG) "has not found evidence that Saddam Hussein possessed WMD in 2003", but left open the possibility that some weapons existed in Iraq, "although not of a militarily significant capability".
Before the invasion, US Vice-President Dick Cheney even alleged that the Iraqi dictator was "reconstituting" nuclear weapons. But Mr Duelfer dismissed that thesis.
Despite Saddam's attempt to retain some parts of the programme after 1991, "during the following 12 years, Iraq's ability to produce a weapon decayed".
Mr Duelfer was introducing the ISG's 1,000-plus page report, based on visits to suspect sites, the examination of thousands of pages of documents and interviews with former Iraqi officials involved in weapons programmes. Moreover, it found no evidence that Saddam had secretly transferred weapons or components to Syria.
Saddam is said to have told interrogators that his previous possession and use of chemical and biological weapons was a key reason why he stayed in power. WMD enabled him halt Iranian attacks in the 1980-1988 Iran/Iraq war, and deterred the US and its allies from marching on Baghdad in 1991.
However, Mr Duelfer did say that only timely Allied action this year had prevented chemical weapons experts from Saddam's regime from linking up with insurgents in Iraq.
He warned that lethal skills developed by Iraqi scientists "could be transferred to other hands". With WMD proven to be a fiction, and increasing doubts about ties between his regime and Osama bin Laden's al-Qa'ida, the risk of proliferation of WMD expertise has become the White House's main argument in defence of the invasion.