However other US military sources played down the importance of the find.

Major Stephen Armes, operations officer of the Marines 1st Battalion, 5th Regiment, said the shells containing suspected blister agents were found Saturday in trailers parked in a schoolyard.

Three were mounted on launchers, he said.

"They tested positive for chemical weapons," he told AFP. But Lieutenant Colonel Fred Padilla, the battalion commander, said more tests were required.

US forces who invaded Iraq on March 20 in a declared bid to strip Baghdad of suspected nuclear, chemical and biological weapons have yet to find what they consider a "smoking gun" that President Saddam Hussein possessed such arms.

Previous reports of chemical weapons finds have turned out to be false upon further analysis.

Armes said Sunday: "We found 278 artillery shells that had blister agents at a schoolyard parked in trailers. Three of them were on launchers."

But Padilla remained prudent, saying only that initial tests had indicated the presence of chemical arms. "The munitions need further analysis," he said.

The US Central Command also played down the discovery saying it was far too early to tell whether the weapons did indeed contain a chemical agent.

"We've had a lot of reports on suspected sites, which turned out to be nothing," a spokesman said at Centcom's forward base in As-Saliyah, Qatar.

"The first testing often means very little," he said.

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SPACE.WIRE