AP: Sarin-Filled Munitions in Iraq Worry U.S., By KATHERINE PFLEGER SHRADER

U.S. officials said Monday they are concerned that other sarin-filled munitions may still exist in Iraq - and may not be well marked - after evidence indicated a roadside shell that exploded contained the nerve agent.

Defense Secretary Donald Rumsfeld said the results were from a field test, which can be imperfect, and more analysis needed to be done. "We have to be careful," he told an audience in Washington Monday afternoon.

Rumsfeld said it many take some time to determine precisely what the chemical was, what its presence means in terms of risks to U.S. forces and other implications.

Meanwhile, the former top U.S. weapons inspector in Iraq, David Kay, said it's possible the shell was an old one overlooked when Iraqi leader Saddam Hussein said he had destroyed such weapons in the mid-1990s. Kay, in a telephone interview with The Associated Press, said he doubted the shell or the nerve agent came from a hidden stockpile, although he didn't rule out that possibility.