Fort Hood gunman 'loved US' - Uncle

Army psychiatrist Nidal Malik Hasan was shot during the gun rampage (AP)

A Palestinian uncle of the Fort Hood shooting suspect said that his nephew loved America and wanted to serve his country, but his work as a military psychiatrist drove him to tears.

The alleged gunman in Thursday's shooting at the Fort Hood military base in Texas, Major Nidal Malik Hasan, was wounded and taken into custody after an exchange of gunfire with two police officers.

At least 13 people died and more than two dozen were wounded.

His uncle Rafik Hamad, 64, said that Hasan, an Army psychiatrist, was emotionally shaken by his work treating US soldiers returning from war zones.

Still, he wanted to serve his country because of the opportunities it had given him as an American, Hamad said.

"I think I saw him with tears in his eyes when he was talking about some of patients, when they came overseas from the battlefield," Hamad said.

Hasan remains in a coma, frustrating attempts to work out what made him kill.

He is said to be in a critical but stable condition as many of his victims continued to fight for their lives in hospital.

Meanwhile investigators resumed their search for a motive to the shooting at Fort Hood, Texas. Witnesses are said to have heard the suspect cry "Allahu Akbar" - Arabic for "God is great" - before opening fire at the sprawling military complex in Texas.

Alleged links to extremist websites were being examined as authorities attempted to work out if Hasan's rampage was driven by mental breakdown or ideological rage.