BAGHDAD -- An Army sergeant who was due to leave Iraq soon after multiple tours has been charged with murder and aggravated assault in the fatal shooting of five fellow soldiers at a military counseling clinic in Baghdad, a U.S. official said Tuesday.

Sgt. John M. Russell was taken into custody outside the clinic following Monday's shooting at Camp Liberty, said Maj. Gen. David Perkins. It was the deadliest case of soldier-on-soldier violence since the Iraq war began in 2003.

Russell, 44, is from Sherman, military officials said.

A military official said he believe Russell had enlisted in 1998, but the record shows that he entered the Army National Guard in 1988 and served in the Guard until 1994. Russell became an active duty soldier in 1994, the record shows. The official spoke to the Associated Press on condition of anonymity because he wasn't authorized to speak on the record.

Russell, according to the official, served in Serbia through the last half of 1996 and Bosnia and Herzegovina in the last half of 1998. Russell received several medals and commendations typical for his rank and time in the military.

Perkins gave few details of the shooting and said there were conflicting accounts of what happened.

He said Russell was referred to the clinic by his superiors, presumably because of concern over his mental state. Perkins said Russell was "probably" on his third tour of Iraq but was due to leave soon.

Perkins said the assailant's weapon had been taken away, but somehow he got a new gun, entered the clinic and opened fire.

In Washington, a Pentagon official said Russell was escorted to the clinic, but once inside argued with the staff and was asked to leave. After he and his escort drove away, Russell apparently seized the escort's weapon and returned to the clinic, said the official, speaking on condition of anonymity because the investigation was ongoing.

He was due to go home in three weeks, the official said.

Perkins said two of the dead were officers from the 55th Medical Company, a reserve unit from Indianapolis. The others were enlisted personnel seeking treatment at the clinic. He did not identify the victims by name.

Russell, of the 54th Engineer Battalion based in Bamberg, Germany, was charged with five counts of murder and one count of aggravated assault in Monday's shooting, Perkins said.

He said a probe has also begun into whether the Army has enough mental health facilities in Iraq, where the attack at Camp Liberty has drawn new attention to the issue of combat stress and frequent deployments to battle zones.

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 emotional problems.

"One thing if we've learned from this war, we learned from World War II, Korea, Vietnam, the previous wars, is not all injuries are physical," said Maj. Gen. Daniel P. Bolger, commander of Multi-National Division-Baghdad.

President Barack Obama, who visited an adjacent base last month, said in a statement that he was "shocked and deeply saddened" by the report.

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.