United States President Donald Trump has ordered the use of a firing squad in the execution of a former army psychiatrist who killed 13 people in a mass shooting at Fort Hood, Texas, in 2009, the Pentagon spokesman has said.

Nidal Hasan, a US citizen of Palestinian descent, would be the first US soldier to be executed by the US military in more than 60 years.

Hasan will be killed by a firing squad under the recommendation of Defense Secretary Pete Hegseth and the approval of the president, Pentagon spokesperson Sean Parnell said in a statement on X on Monday.

The Army secretary will decide a time and place for the execution, he said.

“Judgement day for Hasan has finally come,” Parnell wrote.

Hasan was sentenced to death in August 2013 after a military jury found him guilty of 45 counts of premeditated murder and attempted murder for shooting a handgun in a medical facility at the Texas military base.

The attack killed 12 unarmed active-duty soldiers and a retired serviceman, and wounded 32 others.

Police arrested him at the scene, where he was shot and left partially paralysed.

The shooting took place weeks before Hasan was set to be deployed to Afghanistan.

He said during his court-martial that the shooting was an effort to stop the soldiers from going to Afghanistan and killing his fellow Muslims, and made almost no effort to defend himself.

The Trump administration added death by firing squad as an appropriate method of execution in April, along with gas asphyxiation and electrocution.

Military executions are extremely rare in the US and can only be approved by the president under the Uniform Code of Military Justice. If the order is carried out, he will be the first member of the US military to be executed since 1961.

According to the Death Penalty Information Center, the 1961 execution was carried out by hanging. The apparent last known execution by a US military firing squad was one carried out “by musketry” in November 1945, the center reported.