By Matthew Davis
BBC News, Washington
The US military has defended the role of doctors in refining the coercive interrogation tactics being used on prisoners at Guantanamo Bay.
There is concern about the possible violation of medical ethics
The Pentagon said no inquiry had produced "credible evidence" physicians had taken part in the "inhumane treatment of detainees".
But it admitted "behavioural science consultants" were helping interrogators exploit prisoners' weaknesses.
The news comes amid fresh concern over possible violations of medical ethics.
Authors of a report in the New England Journal of Medicine say that since late 2002, psychiatrists and psychologists have been part of a programme designed to increase fear and distress among prisoners as a means to getting intelligence.
They say there are "strong indications" that Behavioural Science Consultation Teams - known as "biscuit" teams - have had access to detainees' personal health information.
"Wholesale rejection of clinical confidentiality at Guantanamo also runs contrary to settled ethical precepts," their report notes.
Meanwhile, a report in the New York Times quoted former interrogators saying they had received specific guidance on how to increase prisoners' stress levels.
In one example, interrogators were told that a detainee's medical files showed he had a severe phobia of the dark and suggested ways that could be manipulated to induce him to co-operate, the newspaper reported.
Pentagon spokesman Bryan Whitman said in a statement that healthcare personnel had a duty to uphold the humane treatment of detainees.
The UN wants to investigate allegations of torture
But he said medical professionals may have other roles at the prison camp.
"Medical professionals trained in mental health disciplines could serve as behavioural science consultants in order to make assessments of the character, personality, social interactions, and other behavioural characteristics of interrogation subjects," he said.
They could also "advise authorized personnel performing lawful interrogations - not unlike civilian law enforcement practices here in the United States".
But Mr Whitman said these specialists were assigned strictly for those purposes and not involved in direct patient care of detainees.
"Behaviour science consultants may observe, but not conduct or direct, interrogations," he added.
'Living in tropics'
Concern over medical ethics at Guantanamo comes at a sensitive time.
The Bush administration has faced allegations of inmate abuse at the jail and of unjustly detaining suspects.
Amnesty International recently compared it to Soviet-era gulags, and some Republicans have questioned whether it should remain open.
On Wednesday, UN investigators accused the US of stalling over their repeated requests to visit detainees.
The UN says it has evidence that torture has taken place at the prison amid reports that 520 inmates have had mental breakdowns.
The Pentagon said the requests to visit were still "under consideration".
Meanwhile, US Vice-President Dick Cheney on Thursday defended the treatment of prisoners at Guantanamo.
He said they were well treated, well fed and "living in the tropics".