An army officer upset at the prospect of deploying to Iraq opened fire on fellow soldiers at the world's largest military base yesterday in a mass shooting that left 12 people dead and at least 31 wounded.

At least two other men in uniform were initially suspected of involvement in the incident at Fort Hood in Texas, raising fears of a co-ordinated attack.

However base commander Lieutenant General Bob Cone later confirmed there was only one suspected gunman, identified last night as Major Nidal Malik Hasan, a doctor specialising in mental health.

Despite initial reports that he had been killed during the shooting, Lieutenant General Cone said Major Hasan was in fact still alive and in hospital after undergoing surgery for his wounds.

"There was a single shooter that was shot multiple times at the scene," said Lieutenant General Bob Cone, "He was not killed as previously reported. He is currently in custody and in stable condition."

The rampage began at a "soldier readiness centre" used for final medical and dental check-ups for troops about to be sent overseas. Major Hasan, reportedly seen shooting indiscriminately, was said to have expressed misgivings in the past about being deployed to Iraq.

President Obama condemned what he called "a horrific outburst of violence" and said of its victims: "These are men and women who have made the selfless and courageous decision to risk and at times give their lives to protect the rest of us . . . It's difficult enough when we lose these brave Americans in battles overseas. It is horrifying that they should come under fire at an army base on American soil."

Military police surrounded a supermarket on the sprawling base soon after the initial attack had sent soldiers and civilians running for cover. There was confusion about the number of attackers, with reports suggesting that at least one other suspect might have been at large and armed with a high-powered sniper's rifle.

Set in hill country in central Texas, Fort Hood is home to more than 70,000 people - including soldiers' families - from the US 1st Cavalry Division and 4th Infantry Division. It has deployed more troops to American-led military operations in Iraq and Afghanistan than any other base.

The sound of gunfire erupted near the soldier readiness centre at 1.30pm, according to John Carter, a congressional representative for the area.

"I had a man on the scene, who is my regional director and former chaplain at Fort Hood, waiting to go to a graduation ceremony when a soldier came running up to him saying, 'Sir, don't go over there. . . . Somebody is shooting over there'," Mr Carter told MSNBC.

"When the soldier ran by him, he saw the soldier didn't know it, but he was wounded. So, he went into the building and they stopped him, because he had been shot.

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