Washington DC - The Supreme Court on Monday rejected an appeal by accused 9/11 mastermind Khalid Sheikh Mohammed and two alleged accomplices that sought to revive plea deals which were later revoked.

Mohammed and two others charged with involvement in the September 11, 2001 attacks – Walid bin Attash and Mustafa al-Hawsawi – struck pre-trial agreements to avoid the death penalty in 2024, during the administration of President Joe Biden.

After criticism by some victims' families, Biden's defense secretary Lloyd Austin ordered the plea deals to be thrown out, sparking a legal battle over whether or not such a move was permitted.

An appellate court ruled last year that Austin had "acted within the bounds of his legal authority."

A brief, unsigned opinion by the Supreme Court on Monday said it would not take up the appeal.

The trio are among the handful of detainees still held at the notorious Guantanamo US military base in Cuba, and are set to go on trial in June 2028.

Mohammed, also known as "KSM," was considered one of Al-Qaeda leader Osama bin Laden's top lieutenants before he was captured in March 2003 in Pakistan.

Much of the legal jousting in the 9/11 defendants' cases has focused on whether they could be tried fairly after having undergone torture at the hands of the CIA.