BAGHDAD: An American Army sergeant shot and killed five fellow soldiers following an altercation at a military counseling center in Iraq Monday, officials said. The attack drew attention to the issues of combat stress and morale among soldiers serving multiple combat tours over six years of war.

The suspect had been disarmed after an incident at the center but returned with another weapon, according to a senior military official in Washington, who spoke on condition of anonymity because the investigation into the shootings was ongoing.

Attacks on fellow soldiers, known as fraggings, were not uncommon during the Vietnam war but are believed to be rare in Iraq and Afghanistan.

A brief U.S. military statement said the assailant was taken into custody following the 2 p.m. shooting at Camp Liberty, a sprawling U.S. base on the western edge of Baghdad near the city's international airport.

President Barack Obama, who visited an adjacent base last month, said in a statement that he was "shocked and deeply saddened" by the report, adding that "my heart goes out to the families and friends" of all those involved "in this horrible tragedy."

After a meeting with Defense Secretary Robert Gates, Obama said he would make sure "that we fully understand what led to this tragedy" and will do everything possible "to ensure that our men and women in uniform are protected as they serve our country so capably and courageously in harm's way."

The military statement in Baghdad said nobody else was hurt, but military officials in Washington said one person was wounded. The names of the victims and shooter were not released.

Pentagon officials said the shooting happened at a stress clinic, where troops can go for help with the stresses of combat or personal issues. Soldiers routinely carry weapons on Camp Liberty and other bases, but they are supposed to be unloaded.

The military official told The Associated Press that the sergeant had been involved in a verbal altercation at the center. His service weapon was taken from him for his own protection and he was driven back to the center later in the day.

The official said that when the sergeant returned he had another weapon. It was unclear whether he was returning under orders or of his own volition.

Another senior military official said the shooter was a patient at the clinic. The official, who also spoke on condition of anonymity because of the probe, did not know what relationship the shooter had to those he killed. ABC News, without identifying a source, reported that two of the dead were clinic staff and three were soldiers waiting for treatment.

The network also aired video of the stress clinic it said was taken just days ago. It showed the clinic's commander, Lt. Col Beth Salisbury, giving a tour of the clinic and describing certain areas where people cannot carry weapons. Salisbury is from the U.S. Army Reserve 55th Medical Company based in Indianapolis.

At the Pentagon, Adm. Mike Mullen, chairman of the Joint Chiefs of Staff, said the shooting occurred "in a place where individuals were seeking help."

"It does speak to me about the need for us to redouble our efforts in terms of dealing with the stress," Mullen said.

The U.S. military is coping with a growing number of stress cases among soldiers in Iraq and Afghanistan — many of whom are on their third or fourth combat tours. Some studies suggest that about 15 percent of soldiers returning from Iraq suffer from some sort of emotional problems.

With violence declining, many soldiers face new challenges trying to shift from fighting a war to training and mentoring the Iraqis — tasks that often require skills in which they have not been trained.

Adding to the stress, there have been several incidents recently when men dressed as Iraqi soldiers have opened fire on American troops, including an attack in the northern city of Mosul on May 2 when two soldiers and the gunman were killed.

Rep. Harry Mitchell, a member of the House Veterans' Affairs Committee, said the Camp Liberty shooting underscores the "critical need" to reach out to soldiers "suffering from the effects of combat stress and post-traumatic stress disorder."

The death toll from the shooting at the counseling center was the highest for U.S. personnel in a single attack since April 10, when a suicide truck driver killed five American soldiers with a blast near a police headquarters in Mosul.

"Any time we lose one of our own, it affects us all," U.S. spokesman Col. John Robinson said. "Our hearts go out to the families and friends of all the service members involved in this terrible tragedy."

There have been several previous fragging incidents in the Iraq war.

• Last September, Sgt. Joseph Bozicevich, 39, of Minneapolis was detained after allegedly killing two members of his unit south of Baghdad. The case remains under investigation.

• In April 2005, Army Sgt. Hasan Akbar was sentenced to death for killing two officers in Kuwait just before the U.S.-led invasion of Iraq in 2003.

• In June 2005, an Army captain and lieutenant were killed when an anti-personnel mine detonated in the window of their room at the U.S. base in Tikrit. National Guard Staff Sgt. Alberto Martinez was acquitted in the blast.

• Spc. Chris Rolan, an Army medic, was sentenced to 33 years in prison in 2007 for killing a fellow soldier after a night of heavy drinking in Iraq.

• In 2008, Army Cpl. Timothy Ayers was sentenced to two years and four months in prison after pleading guilty to involuntary manslaughter in the fatal 2007 shooting of his platoon sergeant in Iraq.

Also Monday, Iraq's main al-Qaida front group, the Islamic State of Iraq, denied Iraqi government claims that the military had captured its leader, Abu Omar al-Baghdadi, according to the SITE intelligence group. Iraqi authorities said on April 23 that al-Baghdadi was in custody. The U.S. military, which had questioned his existence in the past, did not confirm the capture.

SITE said the group, in a posting on a Web site used by Islamic militants, said that al-Baghdadi was "fine" and that the man whose image was broadcast on Iraqi TV was unknown to them. "All that has been shown is not more than a play," the group said in the posting, the authenticity of which couldn't be verified.

In other violence, the military announced Monday that a U.S. soldier was killed a day earlier when a roadside bomb exploded near his vehicle in Basra province of southern Baghdad.

In the northern city of Kirkuk, a car bombing killed two people Monday, including a 10-year-old boy, and wounded 10 others, police Brig. Gen. Sarhat Qadir said.

In Baghdad, a senior Iraqi traffic officer was assassinated on his way to work. It was the second attack on a high-ranking traffic police officer in the capital in as many days.