Ramzi bin al-Shibh, 51, had been scheduled to be one of five defendants in a trial related to the September 11, 2001, attacks on US cities by Al Qaeda that left almost 3,000 people dead.

But Colonel Matthew McCall, a military judge, said the prisoner was too psychologically damaged to help defend himself, The New York Times reported.

Doctors at the US base on the eastern tip of Cuba diagnosed Ramzi with post-traumatic stress disorder and secondary psychotic features, as well as a delusional disorder.

The military psychiatrists said his condition left him “unable to understand the nature of the proceedings against him or cooperate intelligently” with his legal defence team, the Times reported.

Ramzi has for years complained of being “tormented by invisible forces that caused his bed and cell to vibrate and that stung his genitals, depriving him of sleep,” the paper added.

Ramzi’s defence lawyer has claimed that his client was tortured by the CIA and went insane as a result of what the agency called enhanced interrogation techniques, that included sleep deprivation, waterboarding and beatings.

He had been due to face pretrial proceedings on Friday with Khalid Sheikh Mohammed, believed to be the mastermind of the 9/11 attacks, and three other defendants. Their hearing will proceed as scheduled, the paper said.

Ramzi was accused of helping organise the Al Qaeda cell in Hamburg, Germany, that hijacked one of two passenger jets that crashed into the World Trade Center in New York.

Another suicide airliner attack targeted the Pentagon in Washington, and a fourth plane crashed in rural Pennsylvania when passengers overpowered the hijackers.