In an extraordinary confidential report to the US authorities, the International Committee of the Red Cross (ICRC) said the military guards and interrogators at the prison deliberately used psychological and physical coercion that was "tantamount to torture". It said the treatment it had witnessed had been increasingly "refined and repressive".
The report by the Red Cross - the only independent organisation permitted to visit the prisoners - was written after a visit by its inspection team in June. It said it discovered a system designed to break the will of the 550 prisoners - four of them British citizens - through "humiliating acts, solitary confinement, temperature extremes [and] use of forced positions".
It added: "The construction of such a system whose stated purpose is the production of intelligence cannot be considered other than an intentional system of cruel, unusual and degrading treatment and a form of torture."
The ICRC refused to confirm the authenticity of the report yesterday, the contents of which were reported by the New York Times. While the organisation previously criticised the treatment of prisoners at the camp, it said it could only ensure its continued access to such prisoners around the world by insisting its comments remained private.
"The contents of the ICRC's representations and reports are confidential and for the exclusive attention of the relevant detaining authorities," it said in a statement. "The ICRC uses its exchanges with governments to make clear its concerns and recommendations regarding the situation in places of detention and to demand changes when necessary. Guantanamo Bay is no exception."
But while the report is remarkable for the force of its language, the allegations it makes are not new. Earlier this year, four British prisoners who had been released without charge from the jail after more than two years, compiled a detailed report that alleged inmates were subjected to a regime of Abu Ghraib-style torture, abuse and sexual humiliation.
Louise Christian, a London-based lawyer who represents two of the four Britons still being held, said last night: "I welcome this report but I wish it had come earlier. I know that Martin Mubanga [one of the prisoners] has complained of torture and I know that Feroz Abbasi [another prisoner] says he has been tortured and subjected to religious and sexual humiliation. All these stories are very consistent with one another." She added: "I hope the US government will stand up and take some notice. This is a scandal that will not go away."
The ICRC report also alleges doctors have been assisting interrogators by providing them with information about the mental health of inmates and their vulnerabilities. The Britons released in March claimed that the treatment carried out was carefully choreographed to have maximum impact. Michael Ratner, director of the New York-based Centre for Constitutional Rights, a non-profit group which has filed various lawsuits on behalf of prisoners, said: "This report is remarkable ... [What is happening] is a serious violation of international criminal law.
Larry Di Rita, a spokesman for the Defence Secretary, Donald Rumsfeld, said that the Red Cross officials had "made their view known". "It's their point of view [but it is not shared by the administration]," he said.