But US President George W. Bush stands by his contention that the trailers are evidence that Iraq sought the unconventional arms which he made the primary reason for the US-led invasion, White House spokesman Ari Fleischer said.

The report stems from an agency that was "not as involved" in analyzing the trailers, said Fleischer.

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

Citing a secret internal document, the Times said the State Department declared it was too early to determine that the trucks constituted proof of Iraq's suspected biological weapons program.

The Central Intelligence Agency had made that assertion in a report to the White House, saying 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."

On May 29, Bush declared that weapons banned under United Nations resolutions had been uncovered 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.

The US administration used the threat of Iraq's weapons programs to justify the invasion of Iraq on March 20.

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