An affidavit by a Marine who visited the Guantanamo Bay detention center last month alleges that guards at the prison camp bragged about routinely abusing detainees both physically and mentally.
The Marine's name was removed from the statement before it was released to reporters.
She said she was with a group of guards who laughed while they described routine beatings of prisoners and doing such things as denying privileges to well-behaved prisoners just to make them angry.
In one case, she said a guard described slamming a prisoner's head into a cell door.
A Marine Corps lawyer defending one of the detainees said he has forwarded the affidavit to the Defense Department's inspector general with a statement saying the abuse described violates American and international law.
A spokesman for the joint task force that runs the Guantanamo detention facility says the force will cooperate fully with the inspector general to learn the facts and will take action where misconduct is discovered. The spokesman said abuse or harassment of detainees in any form is not condoned or tolerated at Guantanamo.