"The Iraqi Survey Group confirmed today that a 155-millimeter artillery round containing sarin nerve agent had been found," Kimmitt said. "The round had been rigged as an IED [improvised explosive device] which was discovered by a U.S. force convoy. A detonation occurred before that IED could be rendered inoperable. This produced a very small dispersal of agent."
After more than a year's search, it appeared that the Iraqi Survey Group -- the U.S. team searching for evidence of weapons of mass destruction -- had finally found some on 15 May. But the amount was small, and the significance was not immediately apparent.
Sarin is a clear, odorless liquid that can cause lethal convulsions in those who breathe it or get it on their skin. It was the poison used by the Aum Shinrikyo cult to kill 12 people in an attack on the Tokyo subway in 1995.
The government of Iraq told United Nations inspectors that it had manufactured hundreds of tons of sarin, and that it used the nerve gas during its war with Iran in the 1980s. It also is believed to have been the agent used against Kurds in northern Iraq 10 years ago.
Kimmitt said no one was seriously injured in yesterday's explosion of the shell, but that two people were treated for what he called "minor exposure" to nerve agents. The general said there were no serious injuries apparently because detonating the shell was much less effective in dispersing the nerve gas than had the shell been fired from a cannon.
U.S. Defense Secretary Donald Rumsfeld responded cautiously to the report yesterday, saying it must still be confirmed that the agent was in fact sarin. He said an initial field test for sarin was positive, but that additional tests were being conducted.
Nor was there any immediate evidence that more artillery shells containing nerve agents exist in Iraq, or if the discovery indicates the presence of a significant stockpile of sarin and other unconventional weapons.
As for the strategic significance of the discovery, Rumsfeld said he believes the United States had good reason to conclude that Hussein had weapons of mass destruction. But whether he had them just as the war began, he said, remains a mystery:
"The intelligence information in our country and in other countries that have excellent intelligence-gathering capabilities was that they existed, that the government of Iraq was systematically deceiving the world about what it was doing. There was a great deal of evidence to that effect. We don't now know what actually happened [to make the weapons disappear]," Rumsfeld said.
In January, Danish troops in southern Iraq discovered mortar shells they believed to contain a blister agent. But subsequent tests proved the shells, which apparently dated to the Iran-Iraq War of the 1980s, had no chemical warfare agent.
Some U.S. officials have told The Associated Press that they are concerned that there may be more weaponized sarin in Iraq, and that insurgents who use whatever weapons they can find may not be able to distinguish between ordinary explosives and shells containing deadly poisons.
The agent used in the shell found on 15 May is believed to be old, and therefore lacking much of its original potency. Still, the AP quotes U.S. officials as saying insurgents may be putting themselves and others in danger simply by handling the explosives, let alone detonating them.
But Rumsfeld made it clear that he believes it is too early to say just what threat such weapons may pose.
There are other, political, reasons that the discovery of the sarin-laced shell may be significant, according to Michael O'Hanlon, who specializes in foreign policy and military issues at the Brookings Institution, a private Washington policy research center.
O'Hanlon tells RFE/RL that the discovery of the suspected sarin can have two distinctly different meanings. "One of them is: We didn't need to fight because there was so little of this stuff, and why bother? But the other point is, of course, this is a reminder that he [Hussein] used to have a lot of chemical agents, and if he did destroy them, it's because we [the United States] finally, after many years, managed to convince him," O'Hanlon said.
O'Hanlon says the threat posed by such weapons is still not clear, given the age of the poisons and the likelihood that insurgents may detonate them in ways that were not originally intended.
But O'Hanlon says that if a small arsenal still exists at weapons depots around the country, its potency lies not in its chemical makeup, but in its status as a relic of a dangerous part of Iraq's pre-war past.
"It's not by itself a huge threat. But some people seem to have forgotten he ever had much of this stuff, ever really wanted it, ever used it. And this is one more visible reminder that there used to be a lot of this stuff in Iraq. On the other hand, I think the chances are that there's not much any more," O'Hanlon said.