Two 'clean' trucks - the Iraq WMD evidence so far

A joint report by the CIA and Defence Intelligence Agency released yesterday concluded that two trucks found in northern Iraq equipped with laboratory equipment represented the "strongest evidence to date that Iraq was hiding a biological warfare programme" but it conceded that no traces of biological agents had been found, nor was there any indication that they had been used for that purpose.

The defence secretary, Donald Rumsfeld, had predicted that the questioning of Iraqi scientists would lead to the discovery of biological and chemical weapons, but he has now raised the possibility that that might not happen.

"It's hard to find things in a country that's determined not to have you find them," Mr Rumsfeld told a meeting of foreign affairs experts on Tuesday.

The most inflated pre-war claims about Iraqi weapons of mass destruction were produced by an intelligence unit established in the Pentagon after September 11, which became a channel for claims made by Iraqi defectors to reach the White House.

The Pentagon's faith in Iraqi exiles' assurances that US troops would be embraced by the population - an assumption now widely blamed for grossly inadequate preparations for postwar security - is also under scrutiny.

"A backlash is building on this. Everyone wants to give the administration more time, but as the weeks go by, there is a growing sense of being manipulated, of being lied to," Mr Cirincione said.

"That does two things. An anger builds towards the administration, and people are much less likely to believe them the next time, for example over Iran."