Wall Street Journal: DALLAS -- A U.S. Army major opened fire Thursday on fellow troops at the giant Fort Hood Army Base in central Texas, killing 12 people and wounding at least 31 in one of the worst incidents of soldier-on-soldier violence in U.S. military history.

The officer, Maj. Nidal Malik Hasan, was later shot by security personnel on the sprawling facility. The severity of some of the injuries suggests the death toll could climb. Two other soldiers taken into custody following the deadly rampage were later released, the office of a Texas congressman said. A spokesman for Rep. John Carter says Fort Hood officials informed Rep. Carter's office of the release. Rep. Carter's congressional district includes the Army base.

The motive for the shooting wasn't immediately clear.

The alleged shooter, Maj. Hasan, was a psychiatrist who had been recently promoted to major and transferred to Fort Hood from the Walter Reed Army Medical Center in Washington. Maj. Hasan's professional specialties included post-traumatic stress disorder, combat stress and other emotional issues common to the troops implicated in earlier incidents of military fratricide. He was slated to deploy to Iraq in coming weeks, according to military officials.

An official at the Pentagon said there were indications that Maj. Hasan was deeply upset about the pending assignment. The official cautioned that it was far from clear that the officer chose to act because of the coming deployment.

With at least 13 dead, Thursday's attack was one of the Army's worst single-day losses of life since the start of the wars in Iraq and Afghanistan.

President Barack Obama said in a nationally televised address that the attack on soldiers in the U.S. was particularly unsettling.

"It's difficult enough when we lose these brave Americans in battles overseas," he said. "It is horrifying that they should come under fire at an Army base on American soil."

Fort Hood is the largest U.S. military facility in the world. It houses the 1st Cavalry Division and the First Army Division West, as well as an array of smaller aviation, logistics, and military police units.

More than 45,000 soldiers are assigned to the base--though, typically, many are deployed to Afghanistan or Iraq at any one time. About 9,000 civilians also work at Fort Hood, and thousands of families live on the base and in nearby Killeen, which is about 160 miles southwest of Dallas.

The attack began at about 1:30 p.m. local time at a processing center where soldiers receive medical checkups as they prepare to deploy overseas, officials said.

Lt. Gen. Robert Cone, the top military commander on the base, told reporters that two handguns had been used in the attack. One of the dead was a civilian police officer at the base, he said. Among the wounded, he added, the "extent of the injuries varies significantly."

Other military shootings have been linked to combat stress and emotional problems suffered by soldiers after long and repeat deployments to Iraq and Afghanistan. With the military stretched thin by the wars, many troops have done three, and in some cases four, tours to the war zones.

Last May, Sgt. John M. Russell, who was on his third overseas deployment, grabbed an assault rifle from a fellow soldier before opening fire on the main U.S. military base in Baghdad. Sgt. Russell has since been charged with five counts of murder.

The Army has gotten better at identifying signs of stress in soldiers and getting them help, said Charles Figley, a mental-health professor at Tulane University. But with long deployments, he said, "It clearly is a pressure cooker for these folks."

Fort Hood is home to the Army's Warrior Combat Stress Reset Program, which aims to help soldiers deal with stress and the return to peacetime life.

Copyright © Wall Street Journal. The Associated Press contributed to this report.

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