By CHRIS TORCHIA, Associated Press Writer

BAGHDAD, Iraq - A roadside bomb containing sarin nerve agent exploded near a U.S. military convoy, the U.S. military said Monday. Two people were treated for "minor exposure," but no serious injuries were reported.

"The Iraqi Survey Group confirmed today that a 155-millimeter artillery round containing sarin nerve agent had been found," said Brig. Gen. Mark Kimmitt, the chief military spokesman in Iraq (news - web sites). "The round had been rigged as an IED (improvised explosive device) which was discovered by a U.S. force convoy.

"A detonation occurred before the IED could be rendered inoperable. This produced a very small dispersal of agent," he said.

The incident occurred "a couple of days ago," he said.

The Iraqi Survey Group is a U.S. organization whose task was to search for weapons of mass destruction after the ouster of Saddam Hussein (news - web sites) in last year's invasion.

The round was an old `binary-type' shell in which two chemicals held in separate sections are mixed after firing to produce sarin, Kimmitt said.

He said he believed that insurgents who rigged the artillery shell as a bomb didn't know it contained the nerve agent, and that the dispersal of the nerve agent from such a rigged device was very limited.

"The former regime had declared all such rounds destroyed before the 1991 Gulf War (news - web sites)," Kimmitt said. "Two explosive ordinance team members were treated for minor exposure to nerve agent as a result of the partial detonation of the round."

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 sentence 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.

Nerve gases work by inhibiting key enzymes in the nervous system, blocking their transmission. Small exposures can be treated with antidotes, if administered quickly.

Antidotes to nerve gases similar to sarin are so effective that top poison gas researchers predict they eventually will cease to be a war threat.