WASHINGTON  Medical personnel were deeply involved in the abusive interrogation of terrorist suspects held overseas by the Central Intelligence Agency, including torture, and their participation was a “gross breach of medical ethics,” a long-secret report by the International Committee of the Red Cross concluded.

Based on statements by 14 prisoners who belonged to Al Qaeda and were moved to Guantánamo Bay, Cuba, in late 2006, Red Cross investigators concluded that medical professionals working for the C.I.A. monitored prisoners undergoing waterboarding, apparently to make sure they did not drown. Medical workers were also present when guards confined prisoners in small boxes, shackled their arms to the ceiling, kept them in frigid cells and slammed them repeatedly into walls, the report said.

Facilitating such practices, which the Red Cross described as torture, was a violation of medical ethics even if the medical workers’ intentions had been to prevent death or permanent injury, the report said. But it found that the medical professionals’ role was primarily to support the interrogators, not to protect the prisoners, and that the professionals had “condoned and participated in ill treatment.”

At times, according to the detainees’ accounts, medical workers “gave instructions to interrogators to continue, to adjust or to stop particular methods.”