The Pentagon has announced it will execute a former US Army major by firing squad, the first such military execution in more than 60 years.

Nidal Malik Hasan fatally shot 13 unarmed US soldiers at Fort Hood, Texas, in 2009, injuring another 32. The killings on 5 November 2009 were the deadliest non-combat attack ever carried out on an American military base.

Pentagon spokesperson Sean Parnell announced on Monday that Secretary of Defense Pete Hegseth had made the recommendation and President Donald Trump approved it. The secretary of the Army will set the time and place of the execution.

"Judgement day for Hasan has finally come," Parnell wrote on X.

The attack took place in a crowded medical building where deploying soldiers were awaiting check-ups and vaccines. Hasan, a US Army psychiatrist from Virginia, later admitted in court he was the gunman and apologised for "any mistakes."

During his court-martial in 2013, he said he believed he was protecting Muslims and the Taliban in Afghanistan.

Hasan is currently one of four inmates on the US military's death row.

Under military law, an execution requires approval from the US president, as well as appellate review and a final judgment on its legality before it can proceed.

The US Court of Appeals for the Armed Forces deemed the military death penalty unconstitutional in 1983, but it was reinstated the following year by executive order under then-President Ronald Reagan.

Military executions differ from those carried out at the state level. The majority of executions in the United States are conducted at the state level, with 27 states, the military, and the federal government still retaining capital punishment as a legally available option.

Execution by firing squad is uncommon in the United States. South Carolina carried out a firing squad execution last year, the first for that state and the first use of the method in the country in 15 years. Four other states also permit the use of a firing squad: Idaho, Mississippi, Oklahoma, and Utah.