According to the American Civil Liberties Union (ACLU), court martials are proceeding against dozens of soldiers in Iraq, Afghanistan and Guantanamo Bay.
Many of the cases have been handled discreetly since 2002, and some soldiers have already been released with mere administrative sanctions.
Some 49 internal military documents posted on the ACLU website describe major abuse incidents, most of them relating to Iraq.
The ACLU obtained the documents through the Freedom of Information Act, often after filing lawsuits against the US government for failing to comply.
- Two soldiers who were ordered to kill a prisoner named Yasir Ahmad Al-Haddi in Camp Bucca, a detention site in southern Iraq, in April 2003. An investigation found the soldiers committed no offence.
- On August 2003, US forces arrested Ubaid Raddad during a raid in the city of Tikrit, just north of Baghdad. Days later a US soldier shot and killed Radad. The soldier was demoted and discharged from the army before a murder investigation could get under way.
- In December 2003 one Lutfi Abd al-Karim was found dead in his cell four days after he was detained in apparent good health. A medic that examined the body found multiple wounds, but the on-site commanders ordered not to perform an autopsy, then failed to interview anyone involved or collect physical evidence.
Responding to the ACLU revelations, Pentagon spokesman Lieutenant Colonel John Skinner said "misconduct is simply not tolerated" and that the "policy has always been and will always remain to treat detainees humanely".
The vast majority of US soldiers "are serving honourably, are upholding our standards and our values", said Skinner.
On Tuesday White House spokesman Scott McClellan said President George Bush "expects that if there are allegations of abuse, that those allegations need to be taken seriously".
Even if the documented cases are investigated, ACLU attorney Jameel Jaffer said, "the question is: why is abuse so widespread?"
According to him, "The policymakers created this culture in which abuse was not just acceptable, but at least in some instances encouraged."