U.S. military police killed two detainees at Abu Ghraib prison early Wednesday after a riot broke out in a tent camp at the sprawling facility west of the capital, a military spokesman said.

The brawl was one of the deadliest skirmishes at Abu Ghraib since the U.S. Army began holding suspected insurgents, or security detainees, there last year. Five detainees were wounded by other detainees, said Lt. Col. Barry Johnson, spokesman for detention operations in Iraq.

Johnson said the fight started when a group of detainees with tent poles attacked an individual in Camp Ganci, one of the prison's two outdoor tent compounds. The brawl quickly escalated, drawing 200 to 300 men, he said.

U.S. military police responded by ordering the detainees to stop fighting, Johnson said. The detainees threw rocks at the guards, who fired back with rubber bullets, he said.

"That had no effect on quelling the disturbance," he said. "A decision was made that this detainee's life was at risk, so shotguns aimed at those behind the violence were used."

Johnson said the rules of engagement at the prison allow military police to use deadly force in such a situation. In this case, the noncommissioned officer in charge of the compound gave the permission, he said.

The incident is being investigated, he said, and "the circumstances surrounding that decision" to employ deadly force will be reviewed.

The last time military police at the prison used lethal force to stop a disturbance was on Nov. 24, when three detainees were killed and several injured during a riot in Camp Ganci.

The U.S. military is holding about 2,200 detainees at Abu Ghraib, down from a peak of more than 7,000 earlier this year. Some detainees were abused at Abu Ghraib last fall, and seven soldiers with the 372nd Military Police Company were charged in connection with the incidents.

The abuses occurred in the prison's so-called hard site, cell blocks that have since been taken over by the Iraqi corrections department to house its inmates. The U.S. military has moved all of its detainees to the tent camps on the prison grounds.

Camp Ganci, the older tent camp at Abu Ghraib, is being razed to make way for a new compound that will house detainees being prepared for release. About 500 security detainees are housed in what remains of Camp Ganci; the majority of detainees live in a newer section called Camp Redemption, which has air-conditioned tents and other amenities that Ganci does not.

Tent poles are often used as weapons during altercations in the camps, and the guards who enter the tent compounds to break up the fights are unarmed, their only protection provided by armed guards in watchtowers.

"When you see these guys walking around with tent poles, it's not a good sign," said Sgt. Wassman, who declined to give his first name.

Wassman said tensions often run high in the camps, though they rarely escalate into full-scale riots. "We've got Shiites on one side and Sunnis on the other," he said, "and then you've got people who just don't like someone because he's ugly or got an extra piece of bread."