US President Donald Trump has called off plans to livestream the execution of former US army psychiatrist Nidal Hasan by firing squad.

Trump had previously said he approved of showing online the death of the Fort Hood attacker, while Vice-President JD Vance cast doubt on whether it would happen and said he would not watch it.

As criticism over the public display mounted, Trump said on Thursday that "many very good and well meaning people would rather not watch him die".

"I think streaming the execution for all to see might have been a strong deterrent for the World to witness how America deals with Terrorists and SCUM like Hasan," Trump said.

"He will die, as scheduled, by firing squad, but this event will not be streamed," the president added.

Hasan fatally shot 13 unarmed US soldiers at a military base in Texas in 2009, injuring another 32. His execution by firing squad will be the first military execution in more than 60 years.

Trump said the execution can be viewed in person by the families of the victims.

"They deserve to witness JUSTICE!" Trump said.