The Pentagon, which maintains detainees are treated in accordance with the Geneva Conventions that prohibit the use of torture or abuse, acknowledged it is investigating claims of beatings and other mistreatment at Guantanamo and in Afghanistan, raised by David Hicks.
"There's currently an ongoing investigation into allegations of abuse in the case of David Hicks based on abuse allegations," Major Michael Shavers, a Pentagon spokesman, said.
He said the investigation began before the allegations became public.
Additional investigations into abuse and mistreatment at Guantanamo Bay, as well as other aspects of the detention mission, are also pending, Shavers said.
Hicks' allegations became public on Thursday in an affidavit released by his attorney.
US Senator Jeff Bingaman, a Democrat from New Mexico, called on US Defence Secretary Donald Rumsfeld to explain reports that the government tried to suppress allegations of abuse at US-run detention camps in Afghanistan, Iraq and Guantanamo.
Several documents published this week show that FBI agents sent to Guantanamo warned the government about abuse and mistreatment at the start of the detention mission in 2002, more than a year before a scandal over mistreatment at Iraq's Abu Ghraib prison.
One letter, written by a senior Justice Department official and obtained by The Associated Press, suggested the Pentagon failed to act on the FBI complaints.
US authorities had been informed
by the FBI in 2002 about abuses
Additional documents released by the American Civil Liberties Union obtained through a Freedom of Information Act request show a special operations task force in Iraq sought to silence Defence Intelligence Agency personnel who may have observed abusive interrogations.
"We need to have a full accounting of what has happened in connection with efforts to suppress information," Bingaman said on Friday, a day after he sent the letter to Rumsfeld.
"The main focus has been on abuse allegations, but now it seems pretty clear there were efforts to prevent people from properly reporting incidents of abuse."
No legal access
Hicks, accused of fighting with Afghanistan's ousted Taliban regime, said he and others suffered abuse by US troops in Afghanistan and Guantanamo Bay, where he has been held since January 2002.
He is one of only four men among the nearly 550 detainees who have been charged. Hicks is scheduled to be tried by a military commission in March.
"At one point, a group of detainees, including myself, were subjected to being randomly hit over an eight-hour session while handcuffed and blindfolded"
David Hicks's affidavit
Most of the prisoners being held at the remote outpost have been held without charge or access to attorneys.
"At one point, a group of detainees, including myself, were subjected to being randomly hit over an eight-hour session while handcuffed and blindfolded," Hicks, 29, said in the affidavit sealed in August.
"I have been struck with hands, fists, and other objects, including rifle butts. I have also been kicked."
Hicks also said he was forcibly injected with sedatives, and that troops denied food to prisoners to coerce cooperation with interrogators.
The military has acknowledged 10 cases of abuse since the detention mission began at Guantanamo, including a female interrogator climbing on to a detainee's lap and a detainee whose knees were bruised from being forced to kneel repeatedly.
Those cases are not among three incidents detailed in the July FBI letter to Major-General Donald J Ryder, the army's chief law enforcement officer investigating abuses at the US-run prisons.
The AP-obtained memo documents abuses that included a female interrogator grabbing a detainee's genitals and bending back his thumbs, a prisoner being gagged with duct tape, and an attack dog being used to intimidate a detainee, who later showed "extreme" psychological trauma.