According to the report, the abuse ranged from sleep deprivation and forced nakedness to severe beatings, electric shocks and sexual assault.
A Pentagon spokesman said mechanisms are in place for detainees to report abuse, and credible claims are "thoroughly investigated."
In what is the most detailed medical study released to date of former U.S. detainees, each of the men underwent two days of intensive clinical interviews and psychological and physical examinations. Beyond the evidence of physical abuse, doctors reported that they found extensive lingering psychological trauma.
Seven of the men have contemplated suicide, according Leonard Rubinstein, the president of Physicians for Human Rights.
"I think it was the combination of overwhelming humiliation and isolation and noise and darkness, and statements by guards and interrogators that they would kill their wives and families -- that's why we had so many people say, 'I want to die,'" Rubinstein said. "There was this overwhelming stress and isolation in every conceivable way."
There was also evidence that three of the men had been raped, three had been subjected to electric shock, which doctors were able to substantiate based on the scarring found on the bodies, and nearly all had been severely beaten. "Beatings ... were so severe they knocked people unconscious, knocked their teeth out," Rubinstein said.
The group found signs of the use of stress positions on all of the men. Some say they were hung by their wrists or arms for hours. And, according to Rubinstein, there was a case of a winch being used.
Seven of the men were detained in Iraq in 2003 and 2004. The other four were detained in Afghanistan and later sent to Guantanamo Bay in Cuba between 2001 and 2003. They were all released without charges, the report said.
One of the former detainees, an Iraqi imam and businessman in his late 40s, whom the report cited as "Kamal" (real names were not used), said he was beaten to the point of losing consciousness when he was arrested by U.S. forces in September 2003. He was brought to Abu Ghraib prison in Iraq, where he was kept naked in a cold, dark room for three weeks. According to the report, he was hit with a rifle and stabbed in the cheek with a screwdriver. He says he was also suspended in stress positions 10 times, causing him numbness that lasted for a month. The report says physicians who examined Kamal found physical and psychological evidence to support his claims.
Another former detainee, "Amir," reported being placed in extreme stress positions for hours while he was being held at Abu Ghraib. He was also subjected to sleep deprivation and doused with cold water. According to the report, Amir said on one occasion he was forced to lay face down in urine, while he was kicked and eventually sodomized with a broomstick. He was then forced to "howl like a dog while a soldier urinated on him." Eventually, a soldier stepped on his genitals, causing him to pass out. The report says a physical examination found evidence to corroborate his claims.
Pentagon spokesman Cmdr. Jeffrey Gordon said the claims made in the report by the former detainees "sound dubious." He said there were mechanisms at the detention facilities for detainees to report abuse claims and "all credible allegations of abuse are thoroughly investigated."
Charges of abuse at Abu Ghraib came to light in 2004 after photographs emerged depicting prisoners being humiliated and threatened by guards. Twelve U.S. soldiers eventually faced charges in military courts over the detainee mistreatment.
President Bush has said of the scandal, it was the work of "a few American troops who dishonored our country and disregarded our values."
Gordon would not comment on specific cases highlighted by the group, however, he noted the number of detainees mentioned in the report -- 11 -- is only a small fraction of the more than 770 who passed through Guantanamo alone.
According to Rubenstein, his group made an effort to reach as many former detainees as possible who would agree to go through two days of clinical testing. The 11 men who participated were recommended by lawyers working on behalf of detainees, he said.
The examinations took place between December 2006 and September 2007. In each case, two clinicians -- a doctor and a mental health professional -- examined the individuals. Their findings were reviewed by the group's ethics review board, according to the report.
The report noted the clinicians found no evidence that the detainees deliberately exaggerated their allegations.
Also in the report, the group accused military health professionals of being complicit with the abuse, denying detainees medical care and giving interrogators confidential medical information that they exploited. One detainee with diabetes, Rubinstein said, was given his medication only intermittently.
The report found several differences in the kinds of abuse detainees were subjected to at both Abu Ghraib and Guantanamo Bay.
"People weren't kept naked in Guantanamo ... and there wasn't the kind of gratuitous cruelty that took place in Abu Ghraib," Rubinstein said.
"On the other hand, the period of detention, distance from family, and sense of being in a black hole was much greater in Guantanamo. And interrogations were more intense. In Iraq, they actually threatened people with going to Guantanamo."
Physicians for Human Rights is calling on the administration and Congress to establish an independent commission to "fully investigate and publicly report on" abuse charges at the various detention facilities. The group also is seeking a formal apology and compensation from the government for abused detainees.