BAGHDAD, May 17: A small amount of the nerve agent sarin was found in a shell that exploded in Iraq, the US army said on Monday in the first announcement of discovery of any of the weapons on which Washington made its case for war.

Brig Gen Mark Kimmitt told a news conference the substance had been found in an artillery shell inside a bag discovered by a US convoy a few days ago. The round had exploded, causing a small release of the substance, he said.

"The Iraq Survey Group has confirmed today that a 155 (mm) artillery round containing sarin nerve agent had been found. The round had been rigged as an IED (improvised explosive device) that was discovered by a US force convoy," he said.

"A detonation occurred before the IED be could be rendered inoperable," Kimmitt said, adding that two members of an explosives team had been treated for exposure to the substance.

Kimmitt said the round, designed to mix the sarin in flight, belonged to a class of ordnance that the ousted government of Saddam Hussein claimed to have destroyed before the 1991 Gulf war.

"It is a weapon that we believe was stocked from the ex-regime time, and it had been thought to be an ordinary artillery shell set up to explode like an ordinary IED... when it exploded it indicated that it actually had some sarin in it," he said.

IEDs are bombs usually planted at the side of the road to explode as coalition vehicles pass. The United States launched its invasion of Iraq last year, accusing then-president Saddam Hussein of developing chemical, biological and possibly nuclear weapons. Failure to find such weapons has stirred criticism in the United States and Britain, Washington's closest ally in the war. -Reuters