The International Committee of the Red Cross says medical personnel were involved in the ill treatment and torture of terrorist suspects held by the United States.
The ICRC makes the allegations in a long-secret report that a journalist obtained and revealed in full to the public this week.
The report says medical personnel allegedly were present while detainees underwent waterboarding, a practice that simulates drowning. It says one detainee reported that a medical worker measured his oxygen level to advise whether the treatment should continue.
The document says other detainees said medical personnel recommended whether prisoners should be shackled in a stress standing position for long periods of time.
The ICRC says participation of the health workers in the abusive interrogation techniques was a gross violation of medical ethics. It says, in some cases, the alleged actions of the medical professionals "amounted to participation in torture and/or cruel, inhuman or degrading treatment."
The ICRC says the health personnel's primary purpose appears to have been to serve the interrogation process, and not the patient.
The report is based on interviews Red Cross investigators conducted with 14 prisoners captured overseas, held by the Central Intelligence Agency, and transferred to the Guantanamo Bay detention center in late 2006.
The prisoners include Khalid Sheikh Mohammed, the alleged mastermind of the September 11, 2001 terrorist attacks on the United States.
The Red Cross issued the confidential report in February 2007, but journalist Mark Danner obtained the report and posted excerpts of it last month on the website of The New York Review of Books. The full report was posted Monday.
U.S. President Barack Obama has pledged to close the Guantanamo detention center and said all U.S. interrogations will be guided by the Army Field Manual, which forbids harsh techniques like waterboarding.