The White House said the mistreatment of detainees has never been a policy
Medical examinations of former terror suspects held by US troops showed proof of physical and psychological torture, a US-based human rights group said.
The Physicians for Human Rights group cited beatings, sexual abuse, electric shock, isolation and forced nakedness.
It said the 11 men - all freed without charge from US military jails in Iraq and Guantanamo Bay - were suffering from post-traumatic stress disorder.
The White House maintains that the US has treated all detainees humanely.
The 121-page report said the medical examinations provided "evidence of violation of criminal laws prohibiting torture and of the commission of war crimes by US personnel".
It said that since only 11 detainees were examined the findings could not be "generalised to the treatment of all detainees in US custody".
But it said the evidence was consistent with the findings of other investigations "making it reasonable to conclude that these detainees were not the only ones abused, but are representative of a much larger number of detainees subjected to torture and ill treatment".
The group drew their conclusions from two-day clinical evaluations of each of the men.
Four of the men, arrested in Afghanistan between 2001 and 2003, spent about three years at Guantanamo Bay prison in Cuba before being released without charge.
The remaining seven were detained in Iraq in 2003 and were held at Abu Ghraib prison, until their release later that year or in 2004.
One of the doctors, Allen Keller, said: "As a physician with more than 15 years of experience evaluating and caring for torture victims from all over the world, the torture and abuse these men were subjected to in Abu Ghraib and the resulting trauma are second to none."