FORT HOOD, Texas: A day after a US Army psychiatrist turned his gun on his comrades at the Fort Hood Army Base, starting a shootout that killed 13 people and wounded 30, military officers began piecing together what may have pushed him toward the rampage.

The base commander said on Friday that soldiers who saw the attack reported that the gunman shouted "Allahu Akbar!" before opening fire at the Texas post.

Lieutenant General Robert Cone told NBC's Today show on Friday that the suspected shooter, Major Nidal Malik Hasan, made the comment, which is Arabic for "God is great!" before letting out a barrage of fire.