Three Britons released from Guantanamo Bay published a dossier on Wednesday alleging systematic abuse including being interrogated at gunpoint and photographed naked at the prison.
The claims by the "Tipton Three" - all young Muslims from the central English town of Tipton detained in Afghanistan in 2002 - were the latest in a litany of abuse claims about Guantanamo, particularly from former British detainees.
Rights groups say tactics against terrorism suspects there may have been similar to those at Abu Ghraib jail near Baghdad where US soldiers abused and sexually humiliated Iraqis.
"The account they have given from start to finish of their time in detention is an account of systematic brutality, systematic, perverse attempts to obtain confessions, interrogation ... in ways banned by the international community," said the three's lawyer Gareth Peirce.
The US military denies abuse at Guantanamo.
London has asked Washington to investigate but notes the Britons made no allegations of abuse during diplomats' visits.
The 115-page dossier - obtained by Reuters in London and due to be formally released later in New York - said one of the three, among five Britons freed in March, was quizzed for three hours in Afghanistan under threat of being shot. "One of the US soldiers had a gun to his head and he was told that if he moved they would shoot him" while a British elite SAS interrogator pressed Rhuhel Ahmed to admit he was in Afghanistan for holy war, the report said.
In Afghanistan and at the base, Ahmed and the other two, Shafiq Rasul and Asif Iqbal, say they were repeatedly kicked and beaten, shackled in awkward positions, deprived of sleep, given painful anal searches, forcibly shaved, photographed naked, shown pornography and intimidated by barking dogs.
All three said they gave in and made false confessions of links to al Qaeda and terrorism activities.
"I was left in a room and strobe lighting was put on and very loud music - it was a dance version of Eminem played repeatedly again and again," Iqbal said of one session. One soldier said "you killed my family in the (twin) towers, and now it's time to get you back," he said of another.
Rasul was once asked: "If I wanted to get surface-to-air missiles from someone in Tipton who would I go to?" The three deny they never complained of abuse, with Iqbal claiming a British diplomat took down two pages of allegations.
They said they were not sexually molested but knew others who were. Rats and scorpions frequently came into prison cages.