U.S. troops found about a dozen 55-gallon drums in an open field near this northern Iraqi town, and initial tests indicated one of them contained a mixture of a nerve agent and mustard gas, an American officer said Sunday.

Lt. Col. Ted Martin of the 10th Cavalry Regiment said troops went to the site at midnight Friday after having been alerted by U.S. Special Forces teams, which were suspicious because of the presence of surface-to-air missiles guarding the area.

A chemical team checked the drums, one of which tested positive for cyclosarin (search), a nerve agent, and a blister agent which could have been mustard gas, Martin said.

"I am satisfied that it is sarin," Martin said, adding that further tests were being conducted.

Soldiers also found two mobile laboratories that contained equipment for mixing chemicals, but they appeared to have been ransacked by looters, Martin said.

Martin said another chemical team was being sent to the site for further testing. In the meantime, the drums have been covered with sand and are under guard by 10th Cavalry (search) soldiers, he added.

Since the collapse of Saddam Hussein's regime, there have been several reports of possible chemical weapons (search) finds, none of which are known to have panned out.

Initial tests by Army equipment are designed to favor a positive reading, erring on the side of caution to protect soldiers. Further, more sophisticated tests will be necessary to determine whether the find is evidence of an illegal weapons program.

President Bush ordered the attack on Iraq last month after Saddam refused to acknowledge that he was holding weapons of mass destruction. The Iraqis long insisted that they ended their weapons of mass destruction programs after the 1991 Gulf War.

So far, no conclusive evidence of chemical, biological and nuclear weapons have been reported by coalition forces.

"There are many sites that we look into every day, and when we have confirmed positive results we will provide that information," said Capt. Stewart Upton, a Central Command spokesman at Camp As Sayliyah, Qatar. "We just want to be very cautious that when we go with the information, that when we release nuclear, biological, or chemical information that we're accurate."

Cyclosarin is a variant of the nerve gas that was used in the 1995 attack on the Tokyo subway system by a doomsday cult, in which 12 people died and thousands were sickened.

Exposure to high amounts may lead to loss of muscle control, twitching, paralysis, unconsciousness, convulsions, coma, and death within minutes.