WASHINGTON (CNN) -- The Pentagon said Thursday there was little likelihood that heavy smoke from more than 600 oil well fires set by Iraqi forces in the 1991 Gulf War caused long-term health problems for U.S. troops in and near Kuwait.

The finding was in one of two reports -- the latest in a series of reports on Gulf War Illness -- released by the Pentagon. Neither report found a connection to the mysterious disease.

Researchers and military officials are trying to find the cause for complaints -- ranging from dizziness to memory loss -- made by thousands of American military veterans of the war.

No cause has been identified for what has been broadly termed "Gulf War Illness."

The report on oil well fires says the blazes, which burned for a period of up to nine months in 1991, released numerous pollutants, "some of which have been known, if in sufficient quantities, to cause adverse health effects or disease in humans."

But, the report concludes, "the concentrations of contaminants were at levels below those that are known to cause short- or long-term health effects."

"The results of air quality monitoring programs conducted during this time frame indicated that the concentrations of contaminants in the oil fire smoke, with the exception of particulate matter, were on par with US cities and did not exceed US ambient and occupational air quality standards," the Pentagon said.

The Pentagon said a review of the scientific literature on the potential long-term health effects from exposure to oil fire smoke was conducted by the private RAND Corp. and that RAND concluded that, "even under conditions of a very conservative exposure scenario, the concentrations of contaminants contained in the smoke (other than particulate matter) were much lower than the levels that are currently known to cause disease in the long-term."

Report on chemical alerts

The second report released Thursday was on a number of chemical alerts recorded by the 11th Marine artillery regiment.

It concludes "the numerous chemical alerts recorded by the 11th Marines were most likely due to various factors other than exposure to chemical weapons agents."

The report says, "All of the devices available to Marine units could produce false positive readings in the presence of substances other than CWA [Chemical Weapons Agents]."

It suggested the "false positive readings" were likely caused by oil well fires that produced "high concentrations of smoke and raw petroleum."

The report also says the false alarms were quickly spread by the extensive radio networks that were established to coordinate artillery fire.

"Receiving units could not tell the originating unit, location or cause of the alert and had little choice but to don additional protective gear as a precaution and log the alert as if it was real," it says.

Fires could have interfered with detection

The Pentagon said after it studied written documentation and interviewed witnesses, "investigators cataloged 18 potential [chemical] incidents associated with the 11th Marines. In each case, the investigators judged the chance of agent presence as unlikely."

"In retrospect, it is clear that fallout from the oil well fires could affect detection equipment and could have caused many of the chemical alerts recorded by the 11th Marines," said Bernard Rostker, special assistant for Gulf War illnesses.

The Pentagon said earlier that thousands of U.S. troops may have been exposed to low levels of chemical agents when American military engineers blew up Iraqi rockets after the war. But no link has been established between that possible exposure and the medical complaints.

CNN Military Affairs Correspondent Jamie McIntyre and Reuters contributed to this report.