WASHINGTON - A US congressman asked the Pentagon on Tuesday to explain why the soldier accused in the massacre of 16 Afghan villagers was sent back into combat after earlier suffering a traumatic brain injury in Iraq, as lawmakers questioned how seriously the military deals with the mental health of troops.

The Army staff sergeant accused in Sunday's shooting served three deployments to Iraq before he was sent to Afghanistan last year. The soldier, whose name has not been disclosed publicly, was treated for a traumatic brain injury suffered in a vehicle rollover in 2010 in Iraq, according to a US official.

Representative Bill Pascrell, founder of a US congressional task force on brain injuries, wrote to Defense Secretary Leon Panetta requesting details of the accused soldier's injury, diagnosis, and when and how he was returned to combat duty.

"I am trying to find out basically whether there was a premature 'OK' on this guy," Pascrell, a Democrat, said in a telephone interview.

"This is not to excuse any heinous acts; we are all sickened by it. But dammit, we all have an obligation to prevent these things," Pascrell said. "If this soldier fell through the cracks, does that mean that others have?"

Other lawmakers expressed similar concerns.

"I think there are some serious questions out there about whether or not we are taking seriously, within the armed services, the issue of mental health," said Democratic Senator Patty Murray of Washington state, home to the army base where the accused soldier had been stationed.

Murray, who recently raised questions about post-traumatic stress disorder diagnoses at that base, said she wondered whether the United States is "correctly" sending soldiers back into combat.

'WAR-WEARY'

"I think we are looking at 10 years of war with some pretty war-weary people," Murray told reporters outside the Senate chamber.

Traumatic brain injury (TBI) is head trauma that either temporarily or permanently disrupts the brain's function. It has been one of the most common injuries from the wars in Iraq and Afghanistan in part because vastly improved battlefield medical care has kept alive wounded soldiers who may have died in previous wars.

Asked whether the accused soldier may have been sent back into combat too soon after suffering a brain injury, Democratic Senator Dianne Feinstein said, "The military ought to take a very good look at it."

"A lot of deployments into this kind of action ... and this kind of isolation. It's very hard," added Feinstein, chairwoman of the Senate Intelligence Committee.

The Lewis-McChord base in Tacoma, Washington, where the accused soldier was stationed before deploying to Afghanistan late last year, is home to one of the military's centers for treating TBI.

Mild cases of TBI may pose a greater risk than severe forms years afterward, according to experts. Mild cases are more difficult to diagnose and many soldiers with the condition refuse treatment, said Terri Tanielian, director of the center for military health policy research at the RAND Corp. research institution.

Tanielian oversaw a 2008 report on TBI and post-traumatic stress disorder among members of the US military who served in Iraq or Afghanistan. An estimated 15 percent of troops deployed in Iraq reported suffering a head injury consistent with TBI, according to a study cited in the RAND report.

The RAND study, based on interviews with just under 200,000 service members, found that of those troops reporting a probable traumatic brain injury, 57 percent had not been evaluated by a physician for the condition. The troops cited fear that treatment would not be kept confidential and would hurt military-career advancement, according to the report.

White House spokesman Jay Carney declined to comment on whether the accused soldier should have been deployed back into combat after the earlier brain injury.

Carney said President Barack Obama was aware of the strain that the wars in Iraq and Afghanistan have placed on US troops, and this was one reason he sought to ensure there were enough resources for veterans to get top-notch care in a time of budget scarcity.