A Pentagon investigation into the interrogation of prisoners detained in the war on terror has found its policy did not lead to abuse.
The report said guidance was not always provided
"We found no link between approved interrogation techniques and detainee abuse," the review concluded.
However, the investigation said there were a number of "missed opportunities" in developing interrogation policies.
The review was launched last year after it emerged that prisoners had been abused at Abu Ghraib jail in Iraq.
Human rights campaigners and members of the Senate Armed Services Committee said they were dissatisfied with the findings.
The review examined 187 Pentagon investigations of alleged prisoner abuse in Iraq, Afghanistan and Guantanamo Bay in Cuba.
It identified several failures, including the poor dissemination of guidance on interrogation techniques to field commanders in Iraq and Afghanistan.
But Navy Vice Adm Albert T Church, who authored the report, said: "We cannot say that there would necessarily have been less detainee abuse had these opportunities been acted upon."
He said a new, more restrictive policy on interrogation in Iraq was approved in January, providing "additional safeguards and prohibitions, [and] rectifies ambiguities".
The report found that in Iraq, compliance with official interrogation policy was generally poor, while in Guantanamo Bay it was nearly always exemplary.
Adm Church conceded that commanders in Iraq were likely to be under pressure from superiors to extract useful information from detainees, but he said "a certain amount of pressure is to be expected in a combat environment".
There was no evidence, he said, that "explicit pressure" had been applied from above to use illicit interrogation techniques to achieve results.
He concluded: "It is clear that none of the pictured abuses at Abu Ghraib bear any resemblance to approved policies at any level."
Seven US service personnel have been sentenced for their part in the Abu Ghraib scandal, in which prisoners were photographed being abused.
Members of the Senate Armed Services Committee challenged Adm Church over his findings.
Democrat Carl Levin said the report "doesn't fill many of the significant gaps left by earlier investigations" into cases of detainee abuse.
"I can only conclude that the defence department is not able to assess accountability at senior levels, particularly when investigators are in the chain of command of the officials whose policies and actions they are investigating," he said.
The campaign group Human Rights Watch said the review was tantamount to a cover up.
"This looks like another whitewash. Almost a year after the Abu Ghraib pictures, we still haven't had an independent investigation into the widespread prison abuse by someone not appointed by or subordinate to [Defence] Secretary [Donald] Rumsfeld," spokesman Reed Brody, told Reuters.