President George W. Bush contended the trailers show that Iraq sought the banned arms, Ari Fleischer said.

"The experts have spoken and the judgment of the experts is very clear on this matter," Fleischer said.

Bush based his justification for the US-led war on his contention that Iraq possessed such weapons and so threatened US security.

However, the US State Department said its experts had questioned some conclusions of the Central Intelligence Agency.

The State Department experts were "somewhat cautionary in terms of the kinds of the conclusions that they felt could be reached on that particular information at that moment (and) said there were other questions that need to be considered," State Department spokesman Richard Boucher said.

The New York Times had earlier reported on a secret internal document in which the State Department declared it was too early to determine whether the trucks proved anything.

The Central Intelligence Agency had reported to the White House that the trailers and a mobile laboratory truck seized near Baghdad in late April were "the strongest evidence to date that Iraq was hiding a biological warfare program."

Secretary of State Colin Powell said of the experts: "they were not disagreeing with the intelligence community in the sense that they weren't saying it was not a mobile lab, they just were not quite up in that curve of confidence that the rest of the intelligence community was at."

And Powell insisted "their confidence level is increasing. They still have some questions, and those questions are well known to the CIA. But I have confidence in the judgment of the CIA that they are for the purpose of developing biological weapons. It has been studied very thoroughly."

He also inisted Washington gradually would be able to show it was right.

"Slowly but surely we are providing more evidence that makes the case that we made that day," he said referring to February 5. I think the presentation (at the UN) holds up. I think that this presentation will stand the test of time."

Meanwhile, US officials looked with hope to a recent discovery of materials hidden at the home of a top Iraqi nuclear scientist.

Mahdi Obeidi, granted refuge in the United States, cooperated with US authorities by handing over documents and parts of a centrifuge, which could be used to enrich uranium used to make bombs.

On May 29, Bush declared that weapons banned by UN resolutions had been found in Iraq.

"We discovered weapons-manufacturing facilities that were condemned by the United Nations," Bush told reporters before leaving for a tour of Europe and the Middle East.

"Biological laboratories described by our secretary of state to the whole world that were not supposed to be there, that are a direct violation of the UN resolutions, have been discovered," he said.

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