In another case, US troops in Afghanistan posed for photos of mock executions with hooded and bound prisoners, but other pictures depicting abuse were destroyed to avert public embarrassment after the Abu Ghraib prison scandal in Iraq surfaced in April 2004.
"These documents provide more evidence that abuse was not localised or aberrational, but was widespread and systemic," Jameel Jaffer, a lawyer for the American Civil Liberties Union (ACLU), said on Friday.
"They also provide further evidence that at least in some cases the government is not aggressively investigating credible allegations of abuse."
Several Army Criminal Investigation Command files released by the ACLU detailed previously unknown detainee abuse allegations. The documents were obtained from the government under court order through the Freedom of Information Act.
An Iraqi taken into US custody in Tikrit when his house was raided in September 2003 said Americans, some in civilian clothing, beat him repeatedly, one file showed.
He stated Americans struck him on the head with a rifle, beat him on the stomach, beat him on the leg with a baseball bat, dislocated his arms, stepped on his nose and broke it, shoved an unloaded pistol into his mouth and pulled the trigger, and choked him with a rope.
"These documents provide more evidence that abuse was not localised or aberrational, but was widespread and systemic"
Jameel Jaffer, lawyer for American Civil Liberties Union
While abusing him, the man stated, a US interrogator demanded he confess to crimes and told him: "Today will be the last day in your life."
The file included medical reports confirming he suffered a broken nose, broken leg and abdominal scars. US soldiers questioned in the case said personnel from Task Force 20, a combined CIA-military unit hunting "high-value" fugitives, had interrogated him.
The man said after he reported the abuse, a soldier forced him to sign a statement renouncing the claims if he did not want to be imprisoned indefinitely.
The army investigation was closed after failing to "prove or disprove" crimes were committed, the file stated.
Another file showed the army investigated a compact disc found in July 2004 in a US office in Afghanistan that contained digital images of US soldiers abusing detainees at Fire Base Tycze in southern Afghanistan. The government did not release the actual images, the ACLU said.
Uniformed soldiers were pictured pointing pistols and M-4 rifles at the heads and backs of detainees, the file stated.
Another army file said senior psychological operations officers had seen US special operations troops commit indiscriminate assaults on civilians in May 2004 in two Afghan villages, but an investigation was closed because villagers could not be interviewed as they lived in what was considered a high-threat area.