US President Donald Trump has approved the execution by firing squad of Nidal Hasan, the former Army psychiatrist convicted of killing 13 people in the 2009 Fort Hood shooting in Texas.

The decision means Hasan is set to become the first person executed by the US military since 1961, more than six decades after the last military execution.

According to Channels Television, Defence Secretary Pete Hegseth recommended the firing squad as the method of execution, with Trump subsequently approving the recommendation. The Secretary of the Army is expected to determine the date and location for the execution.

Hasan was sentenced to death by a military jury in 2013 after being convicted over the November 5, 2009 attack at Fort Hood, where he opened fire at a medical facility on the sprawling Army base. The shooting left 13 people dead and more than 30 others wounded.

During his court-martial, Hasan represented himself and did not call witnesses or testify in his defence. Evidence presented during the trial linked his actions to opposition to US military operations in Iraq and Afghanistan, as well as his online communication with cleric Anwar al-Awlaki, who was later killed in a US drone strike in Yemen.