By Aaron Glantz.

SAN FRANCISCO, May 11 (IPS) - A U.S. soldier shot five of his colleagues dead at a base in Baghdad, Iraq Monday. The Pentagon says at least two other people were hurt in the shootings and the gunman is in custody.

Details are still coming in, but the incident reportedly happened at a stress clinic where troops get help for personal issues or combat trauma.

At an afternoon press conference, Secretary of Defence Robert Gates was tight-lipped about the details of the shooting, the first such spree by a U.S. soldier through six years of war in Iraq.

"We're still in the process of gathering information on exactly what happened," Gates said, "but if the preliminary reports are confirmed, such a tragic loss of life at the hands of our own forces is a cause for great and urgent concern."

A military statement said the shooting took place at around 2 p.m. local time in the mental health clinic at Camp Liberty, a sprawling base next to Baghdad International Airport. The Pentagon said the names of the dead soldiers were being withheld pending family notification. The name of the shooter was also not released.

Veterans' advocates say the details of the incident will be critical in assessing whether the killings could have been prevented.

"We need to know if this soldier was examined by a physician before or after deployment and if any mental health symptoms were observed," said Paul Sullivan, executive director of Veterans for Common Sense.

"We know from repeated Congressional investigations and hearings that the military has knowingly sent soldiers with physical and mental health diagnoses and severe symptoms back to the war zones. In some cases, the service members killed themselves or others," he said.

More than 230 active soldiers, airmen and marines committed suicide last year - the highest military suicide statistic in nearly 30 years. In January, more U.S. soldiers killed themselves than died in Iraq and Afghanistan combined.

In November 2006, a New York National Guardsman was arraigned in a military court on charges of murdering two officers in an explosion at one of Saddam Hussein's former palaces.

The series of incidents leaves some observers to recall the military's internal meltdown during the Vietnam War.

"In December of 1972, the Defence Department acknowleged that somewhere between 800 and 1,000 officers had actually been blown up by their subordinates," explained Vietnam war widow Penny Coleman, author of the book 'Flashback: Post Traumatic Stress Disorder: Suicide and the Lessons of War'.

Back then, the killings were called 'fragging', because fragmentation bombs were usually used.

"The fragmentation devices were the weapon of choice because they left no evidence. There were obviously no fingerprints," Coleman said. "There was no way of tracking it."

Iraq war veterans watched the news come in with a mixture of shock, outrage, and resignation.

Former U.S. Army Captain Luis Carlos Montalvan received two Bronze Stars and one Purple Heart for wounds sustained during his two tours in Iraq. He first saw the news in the waiting room in Manhattan's Veterans' Affairs hospital, where Montalvan and his fellow veterans had all been waiting for hours to see a doctor.

"We were just shaking our heads," he said.

Montalvan said many of his fellow veterans felt a mix of irony and horror that while they were waiting for hours to receive government health care stateside, their active duty counterparts were being killed by one of their own in a clinic in the war zone.

"It's horrifying," he added, "that there were men and women in a combat stress centre at Camp Liberty who were going to seek help and now their relatives back home who thought that their loved ones were going to get treatment are dead. They went to get treatment and they're dead. Can you imagine the grief?"

At the Pentagon press conference this afternoon, the head of the Joint Chiefs of Staff, Admiral Mike Mullen, said the military's investigation will include an examination into the number of tours the suspect had served in Iraq and whether he had been deployed to the war zone despite an earlier mental health diagnosis.

Mullen said the shooting spree "does speak to me about the need for us to redouble our efforts in terms of dealing with the stress [of war], dealing with those kinds of things."

After eight years of war in Afghanistan and six years of war in Iraq, the Pentagon reports nearly 800,000 U.S. soldiers have served more than one tour in the war zone. According to the non-partisan Rand Corporation, approximately 300,000 Iraq and Afghanistan war veterans suffer from post-traumatic stress disorder or major depression, while another 320,000 have sustained a traumatic brain injury, physical brain damage often caused by roadside bombs and mortars.

"The first impulse is to be angry at a service member for taking lives, that's the first inclination," Montalvan added, "but then you can't help but ask: 'What caused this person to be this upset, this angry?' And the likely conclusion is that this person could not get help."

*IPS contributor Aaron Glantz is author of "The War Comes Home: Washington's Battle Against America's Veterans" (University of California Press/January 2009).