WASHINGTON: Lawyers for self-confessed September 11 mastermind Khalid Sheikh Mohammed revealed Tuesday that they have asked the UN to investigate their client's alleged torture at Guantanamo Bay military jail.

On the UN's International Day in Support of Victims of Torture, Mohammed's defense team revealed they had sent a “Letter of Allegation” to Juan Mendez, the UN Special Rapporteur on Torture.

The letter was sent on May 5 from Guantanamo, on the eve of Mohammed's arraignment on charges for which he faces the death penalty.

The first confessions of the Pakistani national, alias KSM, who has claimed responsibility for the 2001 attacks, were obtained under torture, after 183 instances of water boarding and 7.5 straight days of sleep deprivation in a secret CIA prison, according to a US intelligence report.

The letter asks that the special UN rapporteur “initiate a full, fair and impartial inquiry” into both US conduct and that of “any other potentially complicit state party to the Convention (against Torture). After subjecting Mohammed to torture and cruel, inhuman and degrading treatment following his capture on March 1, 2003 in Rawalpindi, Pakistan, the US government has silenced him,” reads the letter, a copy of which was obtained by AFP.

“No one without a top secret security clearance is allowed to meet with him or speak to him. His defense attorneys are told to treat his every word as ‘presumptively top secret',” the letter adds, inviting Mendez to meet the most famous detainee at Guantanamo.

“The US government seeks to close this painful and dark chapter in our Nation's history by killing Mohammed after a show trial,” it claims.

“No human being should be tortured,” wrote Captain Jason Wright, a military lawyer assigned to Mohammed, wrote in today's release.

“In the period since 9/11, the US has misplaced its moral compass. Through accountability, we can hopefully find our way again, and pursue a path of rediscovery and redemption.”