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.
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.”