US prosecutors have secured a plea deal with 9/11 mastermind Khalid Sheikh Mohammed, according to the Pentagon.

The agreement includes Mohammed, Walid bin Attash, and Mustafa al-Hawsawi pleading guilty to conspiracy, thereby avoiding a death penalty trial.

Specific details are withheld, but the deal moves their cases towards resolution, which have been delayed for years due to pre-trial processes at the Guantanamo Bay military base.

Guantanamo was used post-September 11 to detain militants away from US legal rights.

The facility, which held 800 prisoners at its peak, remains open despite President Joe Biden's pledge to close it.