A military jury has sentenced a U.S. Army psychiatrist to death for the 2009 mass murder of 13 people, mostly unarmed soldiers, at Fort Hood, Texas, which the convicted gunman said he committed in retaliation for U.S. wars in the Muslim world.

Major Nidal Hasan, who shouted "Allahu akbar" during the attack and later said he wanted to be a martyr, faces death by lethal injection for a rampage that also wounded 31 people at the sprawling central Texas military base, where he opened fire just weeks before he was to be deployed to Afghanistan.

Such sentences are rare in the military, which last executed a member of the armed services 52 years ago. Hasan, 42, becomes the sixth man on death row at the U.S. military's prison at Fort Leavenworth, Kansas.

The military jury of 13 officers who previously convicted Hasan of killing 13 people and wounding 31 others, most of them unarmed soldiers, deliberated for just over two hours before returning its decision.

Hasan opened fire in a medical facility on the Texas base, one of the largest in the United States, on November 5, 2009, just weeks before he was to be deployed to Afghanistan.

He said in his opening statement on Aug. 6 that he was the gunman and had switched sides in what he considered to be a U.S. war on Islam. An Army psychiatrist, he said nothing to the jury since then regarding his motives.

Witnesses testified Hasan, an American-born Muslim, screamed "Allahu akbar" ("God is greatest" in Arabic) as he sprayed gunfire with his laser-sighted handgun.

The death sentence for Hasan sets off an automatic and lengthy appeals process, typically a minimum of four years, according to military officials. A military execution would require the approval of the Fort Hood commanding general and the U.S. president in order to take place.