WASHINGTON (CNN) -- For the first time since beginning research into Gulf War Syndrome, the Pentagon said Tuesday that it could not rule out a particular drug as the cause of a wide range of ailments in Gulf War veterans.

Officials cautioned that this did not prove that the drug did harm the troops, just that it cannot be discounted as a possible causative agent.  Previous studies have ruled out oil well fires, depleted uranium shells and stress as probable causes.

Drug is protection against nerve gas

The drug in question in the latest report is pyriostigmine bromide -- or PB -- which was given to an estimated 25,000 U.S. troops as a way to increase the effectiveness of treatments against a particular nerve agent known as soman.

"Iraq was known to have nerve agents available and militarized, and had used them against Iran and the Kurds," Dr. Beatrice Golomb, the study's primary author said, adding that it was also known that the Soviets had soman and may have made it available to Iraq.

The Pentagon financed the review of scientific literature on PB that resulted in the 358-page report by the RAND Corp., a California think tank.