BAGHDAD - American soldiers tortured Iraqi prisoners at a military base in Mosul but nobody was court martialed over the abuse, U.S. army documents say.

The documents show that mistreatment of Iraqi prisoners was not confined to the Abu Ghraib jail, where abuse and sexual humiliation of inmates caused worldwide outrage last year.

An investigation by a U.S. officer after an Iraqi prisoner's jaw was broken at the base in Mosul found that "detainees were being systematically and intentionally mistreated" in late 2003.

Inmates were hit with water bottles, forced to do exhausting physical exercises until they collapsed, deprived of sleep and subjected to deafening noise, the investigation report found.

One prisoner died in December 2003 after four days of repeatedly having to do physical exercises as a punishment, according to the documents, obtained by the American Civil Liberties Union under the Freedom of Information Act.

The Mosul investigation began after 20-year-old Salah Salih Jassim had his jaw broken in detention. He was not suspected of any crime but had been arrested along with his father, an officer in Saddam Hussein's Fedayeen militia.

"All night they were throwing water on us and making us stand and squat. From the night to the next day ... they were beating us," Jassim said in testimony to investigators.

"IT SMELLED BAD"

The investigation report said Jassim was held in a detention room with around 70 other prisoners. Deafening heavy metal music was played, and guards threw cold water onto hooded prisoners and sounded bullhorns beside their heads.

"It smelled bad. I saw one guy banging his head against the wall, all on his own," one of the U.S. guards testified. Another said several guards had lost their voices from yelling.

"The guards in the room were roaming among the detainees pounding on metal doors, shouting at the detainees to perform exercises, and physically grabbing detainees if they were slow getting to their feet," the report said.

"The detainees had sandbags over their heads that were marked with different crimes, leading the guards to believe that the particular detainee committed that particular crime."

The report said the bag on Jassim's head was marked 'IED' -- the acronym for Improvised Explosive Device, roadside bombs that have killed and maimed hundreds of soldiers.

Planting IEDs is "a particularly hated crime by infantry soldiers patrolling the streets," the report noted.

Soldiers who were in the room when Jassim's jaw was broken all said they did not see the incident. The investigation concluded that Jassim was most probably hit in the face, or that he may have fallen on his face as a result of exhaustion.

Soldiers questioned for the investigation revealed a culture of prisoner abuse at the base. One said that troops "always harassed the hell out of detainees." Another said that at times "the detainees would get so scared they would piss themselves."

The investigation was unable to determine which guards were at fault, so none were punished. But the investigating officer said many of his recommendations for improvements were implemented, including ceasing physical harassment of prisoners and putting the detention room under military police control.

The Pentagon says abuse of prisoners in Iraq was carried out only by a few rogue soldiers, and that all accusations of abuse are thoroughly and promptly investigated. The U.S. government says it has never authorized the use of torture.

U.S. military documents released under the Freedom of Information Act show that scores of accusations of abuse have been investigated in Iraq, Afghanistan and Guantanamo Bay.

Earlier this month, the Pentagon said it would not reopen an investigation into allegations by three Iraqis working for Reuters that they were subjected to beatings, sexual humiliation, sleep deprivation, white noise and exhausting physical exercises at a U.S. base near Falluja in January 2004.

Reuters says the investigation, for which none of the Iraqis was interviewed, was inadequate and should be reopened.