Soldiers who removed the bomb experienced symptoms consistent with low-level nerve agent exposure, U.S. officials said. No one was wounded in the partial blast Saturday, and the dispersal of sarin from the bomb was very limited, the military said.
If confirmed in subsequent testing, the discovery would be the first evidence of a banned weapon in Iraq since the war began. The Bush administration based its case for the war on the existence of such weapons.
Earlier this month, some trace residue of mustard agent, an older type of chemical weapon, was detected in an artillery shell found in a Baghdad street, a U.S. official said Monday, speaking on condition of anonymity. The shell was believed to be from one of Saddam's old stockpiles and was not regarded as evidence of recent weapons of mass destruction production in Iraq.
In Washington, Defense Secretary Donald H. Rumsfeld cautioned that the sarin 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.
U.S. troops have announced the discovery of other chemical weapons before, only to see them disproved by later tests. Deputy State Department spokesman Adam Ereli said "the jury is still out" on whether chemical or other weapons of mass destruction remained in Iraq.
The former top U.S. weapons inspector in Iraq, David Kay, said it was possible the shell was an old relic overlooked when Saddam 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.
Former U.N. weapons inspector Hans Blix, speaking to the AP in Sweden, agreed the shell was likely a stray weapon scavenged from a dump and did not signify that Iraq had large stockpiles.
Numerous arsenals and weapons depots were looted in the turmoil following the collapse of the regime last April. Some depots are still only lightly guarded. Many of the materials used for roadside bombs were believed to have been looted.
Brig. Gen. Mark Kimmitt said he believed that insurgents who planted the explosive did not know it contained the nerve agent. The 155-mm shell did not have markings to indicate it contained a chemical agent, a U.S. official said.
He said a U.S. military convoy discovered the round, which had been rigged as an explosive device. A detonation took place before soldiers could make the bomb inoperable, producing "a very small dispersal of agent."
U.S. officials believe, based on evidence, that the shell was an experimental munition produced before the 1991 Gulf War, called a binary type — a bomb carrying two separate chemicals that when combined in an explosion, produce sarin.
Dispersal would be far more effective if a shell containing nerve agent were fired from an artillery piece, Kimmitt said.
Even so, it appears that two components in the shell that exploded Saturday did not properly mix upon detonation, the U.S. official said.
Blix, whose inspection team didn't make any significant weapons finds during months of searching Iraq before the war, said he and his team found 16 warheads that were tagged as used for containing sarin but were empty.
Saddam's government had disclosed binary sarin testing and production after the 1995 defection of Iraqi weapons chief Lt. Gen. Hussein Kamel al-Majid, Saddam's son-in-law. But Saddam's government never declared that any sarin or sarin-filled shells still remained.
Iraq used the chemical during its war with Iran in the 1980s and is believed to have used it against Kurdish Iraqi civilians. According to U.N. weapons inspectors, sarin-type agents constituted a significant part of Iraq's chemical weapons arsenal — about 20 percent of all chemical weapons agents that Saddam's government declared it had produced.
Nerve gases inhibit key enzymes in the nervous system, blocking their transmission. In large enough doses, sarin causes convulsions, paralysis, loss of consciousness and potentially fatal respiratory failure. Small exposures can be treated with antidotes, if administered quickly.
In 1995, Japan's Aum Shinrikyo cult unleashed sarin gas in Tokyo's subways, killing 12 people and sickening thousands. In February of this year, Japanese courts convicted the cult's former leader, Shoko Asahara, and sentenced him to be executed.
Developed in the mid-1930s by Nazi scientists, a single drop of sarin can cause quick, agonizing choking death. There are no known instances of the Nazis actually using the gas, but that didn't stop other nations from stocking it.
While the finding an artillery shell designed to disperse the nerve gas sarin is notable, it would take an arsenal of such weapons to pose a meaningful military threat, arms policy experts said.
"You would fire hundreds of these shells on the battlefield to have any significant effect," said Jonathan B. Tucker, a senior researcher at the Monterey Institute's Center for Nonproliferation Studies in Washington.
In that way "you try to saturate an area" containing enemy troops, said Michael Powers, a senior fellow at the Chemical and Biological Arms Control Institute in Washington.
U.S. military officials in Baghdad said the Iraq Survey Group, a U.S.-led organization whose task was to search for weapons of mass destruction after the ouster of Saddam, confirmed the presence of sarin.
The team has run into a number of dead ends. In January, for example, field tests on discovered mortar shells near Qurnah in southern Iraq indicated a blister agent was in the shells. But follow-up tests indicated that the munitions did not contain the agents, though U.S. officials said Saddam had such agents in the early to mid-1990s.
Officials say there are chemicals associated with certain munitions, such as phosphorous, that can produce false positives. Some field tests are designed to favor a positive reading, erring on the side of caution to protect soldiers.
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