In its central conclusion, the Senate veterans affairs committee - made up of both Republicans and Democrats - supported the US military's assessment that there was no single cause for the syndrome.

It also agreed with the Pentagon in saying that there was insufficient evidence to conclude that exposure to chemical weapons was to blame.

Swallowing an anti-nerve gas tablet - Did it protect or do harm?

However, one of the chairmen of the committee said that he personally believed that nerve gas, to which some soldiers were exposed when an Iraqi dump was blown up, was a factor in the illnesses reported.

Military 'grossly delinquent'

The report is highly critical of the Pentagon's chemical and biological warfare precautions.

One of the chairmen - Republican Senator Arlen Specter - said that the military had been grossly delinquent.

Preparations had been inadequate and medical record-keeping poor. Senator Specter said that American troops were still unprepared.

In response, a Pentagon spokeswoman said that lessons had been learned.