FORT HOOD, November 7, 2009 (AFP) - Soldiers and medical personnel at Fort Hood, Texas, one of the nation's busiest posts, recounted a tale of horror following the terrifying rampage here when a lone gunman fired on scores of soldiers.

The troops, all war veterans, told reporters Frida that they saw carnage and confusion rivaling their worst days in Iraq.

But they singled out a petite, tenacious Fort Hood civilian police officer for preventing the toll from being far higher than Thursday's 13 dead and 30 injured.

Kimberly Munley, 34, was directing traffic when the first shots rang out in the early afternoon. She rushed to the scene and challenged the alleged shooter, psychiatrist Major Nidal Malik Hasan, by pumping two rounds into him from her handgun.

Hasan charged at the woman, firing back, and both fell in a hail of gunfire that sparked what one witness called "controlled chaos."

Soldiers were ripping off shirts to use them as pressure bandages to stop the bleeding of the wounded.

Army Chief of Staff George Casey told reporters that one soldier dragged four wounded comrades to his pickup truck and drove them to Darnall Army Community Hospital, the post's medical center.

Neither Casey nor Army Secretary John McHugh revealed details about the 39-year-old psychiatrist thought to have been the lone assailant.

Hasan, a Virginia native, was shot multiple times by Munley, a weapons expert and member of the post's SWAT team.

He was in stable condition late Friday at Brooke Army Medical Center, spokesman Dewey Mitchell said, declining to reveal other details of his condition or injuries.

Witnesses at the shooting scene and at the Fort Hood hospital described the attack as a virtual replay of their own experiences in Iraq.

Veterans call the mass casualty events "mas cals," but this one was different in a significant way -- most victims in Iraq suffer burns and trauma as a result of powerful bombs, but the Fort Hood victims all suffered bullet wounds.

One witness, private Marquest Smith, said he saw Hasan walk between hundreds of soldiers standing in rows at Fort Hood's Soldier Readiness Center, firing at them with two handguns.

Soldiers returning from the war zone and preparing to deploy receive medical and mental assessments here, among other things.

"I feel very betrayed," said Smith, 21, from Fort Worth, Texas.

"He was in uniform. He was supposed to be in the fight with us, not against us."

Andrew Hagerman, a 27-year-old military police officer from Lewisville, Texas, was patrolling a residential area on the post when he heard a report of gunshots.

A few moments later he saw Hasan, shirtless and in combat pants, on the ground. Hasan was wounded and unconscious.

"You don't ever expect to see this when you're at home," said Hagerman, a two-tour veteran of Iraq.

Howard Appleby, a 31-year-old Jamaican on his way to see a psychiatrist treating him for Post-Traumatic Stress Disorder, said he had flashbacks of his two Iraq deployments while taking wounded troops out of ambulances.

When asked to describe the flashbacks, he replied, "I don't even want to talk about it."

US President Barack Obama led his nation in mourning Friday as shocked Americans struggled to understand why a Muslim army doctor unleashed a massacre at a US military base, killing 13.

Alleged shooter Major Nidal Malik Hasan, 39, a psychiatrist and specialist in combat stress who had been about to deploy to Afghanistan against his wishes, also wounded 30 people in Thursday's deadly rampage.

Speculation swirled at Fort Hood, Texas Friday as to whether the alleged shooter Hasan had snapped under the pressure of his job counseling thousands of war-weary troops, or was motivated by deeper convictions.

Obama cautioned against making hasty assumptions as an investigation was launched.

"We don't know all of the answers yet. I would caution against jumping to conclusions until we have all of the facts," he said.

"What we do know is that their families, friends, and an entire nation is grieving right now for the valued men and women that came under attack," Obama said.

He ordered flags to fly at half-staff at the White House and federal buildings, as troops here and around the world held a minute's silence to mourn the dead.

Obama would also attend a memorial service due to be held in the coming days, the White House said.

The bodies of those killed were taken to the same mortuary at Dover Air Base in Delaware that handles fallen soldiers from the wars in Afghanistan and Iraq, the Pentagon said Friday.

Hasan was moved meanwhile from a civilian to a military hospital, in part for security reasons, Fort Hood deputy commander Colonel John Rossi told reporters.

Army chief of staff General George Casey said the attack was "a kick in the gut, not only for the Fort Hood community but for the entire army."

Hasan was shot and seriously wounded by a female civilian police officer who was being hailed as a heroine for ending his deadly rampage. He remained on a ventilator in a civilian hospital Friday.

Witnesses reportedly heard him shout "Allahu Akbar!" (God is greatest) as he opened fire in a troop processing center with a semiautomatic weapon and a handgun.

Rossi said investigators believe Hasan fired more than 100 rounds during the incident, and that that accounted for the high number of casualties.

Although "Allahu Akbar" is a Muslim prayer, it has come to be associated with Islamic militants as they carry out attacks or suicide bombings.

A surveillance video aired by CNN showed the major buying breakfast wearing traditional Muslim garb at a base store just hours before the shooting.

The bloodshed dealt a new blow to US forces already under severe strain from repeated combat tours and plagued by a rise in suicides and depression.

Fort Hood, by area the world's largest US military base, has borne the brunt of the wars in Iraq and Afghanistan. Troops based here have suffered the highest number of casualties and have undertaken multiple tours of duty.

Amid the sorrow, the shooting raised delicate questions about Muslim soldiers serving in the US Army, as some Muslim groups feared a huge backlash.

Casey, the army chief of staff, said after a visit to the base that he, too, feared that possibility.

"One of the reasons I told our leaders to keep their people informed and not rush to judgment or speculate until the investigation comes out, I do worry slightly about a potential backlash and we have to be all concerned about that," he said.

Hasan was born in the United States to Palestinian parents who had moved from a small town near Jerusalem.

His cousin Nader Hasan, writing on behalf of the family as Hasan's parents are dead, said they were stunned by Thursday's events and stressed they all considered themselves Americans.

"Our family loves America. We are proud of our country, and saddened by today's tragedy," Nader Hasan said in the message posted on The Washington Post website.

Nidal Hasan's aunt, Noel Hasan, told the daily her nephew had been subjected to harassment about his faith since the September 11, 2001 attacks and had repeatedly sought to be discharged.

An unsigned video praising the attack appeared on a Islamic militant website called the Fallujah forum on Friday, and was swiftly picked up by other sites.

The Muslim military officer suspected in the shooting deaths of 13 people here was transferred Friday from a civilian to a military hospital in part for security reasons, a military official said.

Major Nidal Hasan, who was shot by police to stop a rampage Thursday at Fort Hood, was moved to the Brooke Army Medical Center in San Antonio Texas, said Colonel John Rossi, the base's deputy commander.

"The suspect Major Hasan was transported today approximately (at) 3:00 pm to Brook Army Medical Center," he told reporters.

Rossi said investigators believe Hasan fired more than 100 rounds during the incident, and that that accounted for the high number of casualties.

Based on cartridges recovered at the scene, Rossi said "all indications are this is not a friendly fire incident."

He said the victims were shot in an enclosed troops processing center, but Hasan was gunned down in an open area by two civilian police officers, one of whom was also wounded but was in stable condition.

Of 30 people wounded in the attack, 23 remained hospitalized, about half of them in intensive care, he said.

President Barack Obama Friday ordered flags to fly at half-staff to honor the 13 people killed on a Texas army base, but urged Americans not to jump to conclusions about why the attack occurred.

"From now until Veterans Day I ordered the flags at the White House and other federal buildings to be flown at half-staff," Obama said, referring to November 11 when the nation remembers those killed in wartime.

"This is a modest tribute to those who lost their lives even as many were preparing to risk their lives for their country."

The US president said he had been briefed Friday by FBI chief Robert Mueller and other agencies after the attack at Fort Hood blamed on a Muslim army psychiatrist that left 13 dead and 30 wounded.

"We don't know all of the answers yet. I would caution against jumping to conclusions until we have all of the facts," Obama added.

"What we do know is that their families, friends, and an entire nation is grieving right now for the valued men and women that came under attack yesterday in one of the worst mass shootings ever to take place on an American military base."

Obama vowed the US administration would provide regular updates as the investigation into Thursday's attack unfolds.

He added that he honored the service of all military personnel. "We stand in awe of their sacrifice and we pray for the safety of those who fight and for the families of those who have fallen."

Major Nidal Hasan, the shooter who killed 12 people at a Texas military base, is still alive and in hospital after undergoing surgery for his wounds, the base commander said Thursday.

"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."

Cone said a "female civilian officer" was thought to be the first responder who shot the suspect.

The shooting took place as soldiers were awaiting medical and dental treatment at a processing center at Fort Hood for troops being deployed on missions to Iraq and Afghanistan, he said.

The "preponderance" of the victims were military personnel, but there were also two civilians involved, Cone added.

Further bloodshed was narrowly prevented when the gunman was apparently blocked from reaching a graduation ceremony attended by some 600 people, just meters away from the scene.

"Thanks to the quick reaction of several soldiers, they were able to close off the doors to that auditorium," Cone said.

After interviewing over 100 people at the scene investigators now appear to have ruled out the possibility that Hasan acted with an accomplice.

"There were initially three were held. All have been interviewed, and at this time we believe the evidence indicates it was a single shooter."

The US Congress held a moment of silence late Thursday in somber acknowledgement of the shooting rampage that left 12 people dead and 31 wounded at the sprawling Fort Hood military base in Texas.

The Senate and House of Representatives paused briefly at the request of lawmakers from the state, Republican Senator Kay Bailey Hutchison and Representative John Carter, whose district is home to the installation.

One American soldier opened fire with two handguns in a busy processing center where troops go before being deployed on overseas missions in Iraq and Afghanistan, killing 11 people, US military officials said.

He was shot dead, and two other soldiers were arrested after the shooting spree and were being held as suspects, said Lieutenant General Bob Cone, commander at Fort Hood, the largest US military base in the world.