Doctors and psychologists the CIA employed to monitor its "enhanced interrogation" of terror suspects came close to, and may even have committed, unlawful human experimentation, a medical ethics watchdog has alleged.

Physicians for Human Rights (PHR), a not-for-profit group that has investigated the role of medical personnel in alleged incidents of torture at Guantánamo, Abu Ghraib, Bagram and other US detention sites, accuses doctors of being far more involved than hitherto understood.

PHR says health professionals participated at every stage in the development, implementation and legal justification of what it calls the CIA's secret "torture programme".

The American Medical Association, the largest body of physicians in the US, said it was in open dialogue with the Obama administration and other government agencies over the role of doctors. "The participation of physicians in torture and interrogation is a violation of core ethical values," it said.

The most incendiary accusation of PHR's latest report, Aiding Torture, is that doctors actively monitored the CIA's interrogation techniques with a view to determining their effectiveness, using detainees as human subjects without their consent. The report concludes that such data gathering was "a practice that approaches unlawful experimentation".

Human experimentation without consent has been prohibited in any setting since 1947, when the Nuremberg Code, which resulted from the prosecution of Nazi doctors, set down 10 sacrosanct principles. The code states that voluntary consent of subjects is essential and that all unnecessary physical and mental suffering should be avoided.

The Geneva conventions also ban medical experiments on prisoners and prisoners of war, which they describe as "grave breaches". Under CIA guidelines, doctors and psychologists were required to be present during the use of so-called enhanced interrogation techniques on detainees.

In April, a leaked report from the International Committee of the Red Cross found that medical staff employed by the CIA had been present during waterboarding, and had even used what appeared to be a pulse oxymeter, placed on the prisoner's finger to monitor his oxygen saturation during the procedure. The Red Cross condemned such activities as a "gross breach of medical ethics". PHR has based its accusation of possible experimentation on the 2004 report of the CIA's own inspector general into the agency's interrogation methods, which was finally published two weeks ago after pressure from the courts.

An appendix to the report, marked "top secret", provides guidelines to employees of the CIA's internal Office of Medical Services "supporting the detention of terrorists turned over to the CIA for interrogation".

Medical workers are given the task of "assessing and monitoring the health of all agency detainees" subjected to enhanced techniques. These techniques include facial slaps, sleep deprivation, walling – where their padded heads are banged against walls – confinement in boxes, and waterboarding or simulated drowning.

The guidelines instruct doctors to carry out regular medical checks of detainees. They must ensure that prisoners receive enough food, though diet "need not be palatable", and monitor their body temperature when placed in "uncomfortably cool environments, ranging from hours to days".

The most controversial guideline refers to waterboarding, the technique where prisoners are made to feel as though they are drowning by having water poured over a cloth across their face. The guidelines stress that the method carries physical risks, particularly "by days three to five of an aggressive programme".

PHR is calling for an official investigation into the role of doctors in the CIA's now widely discredited programme. It wants to know exactly how many doctors participated, what they did, what records they kept and the science that they applied.

• Physicians for Human Rights is a not-for-profit group