The US military has extended by four weeks its investigation into FBI allegations that prisoners were tortured at the Guantanamo detention camp, saying it needed more time to question witnesses in several countries.

The lawyer for Mamdouh Habib has alleged his client was tortured while at the prison camp. Mr Habib was released without charge last week.

Adelaide man David Hicks is still being held at the camp.

The military's Southern Command, which oversees the controversial camp for foreign terrorism suspects at the US Naval base in Guantanamo Bay, Cuba, had asked two officers to investigate and report back by February 1.

SouthCom's commander, General Bantz Craddock, extended the deadline to February 28 and said further extensions could not be ruled out because the investigators need to reach widely scattered witnesses who had been at Guantanamo.

"These witnesses are located from Maine to California, nationally, and from Iraq to Korea, internationally," Gen Craddock said in a written statement.

The allegations date back to 2002, the year the camp opened, and military personnel, interrogators and FBI agents have regularly rotated through Guantanamo since then.

Gen Craddock ordered the investigation last month after the public release of FBI documents that described prisoners shackled in a foetal position on the floor for up to 24 hours and left in their own urine and faeces.

One described an interrogation in which a prisoner was wrapped in an Israeli flag and bombarded with loud music and strobe light. Another reported seeing a barely conscious prisoner who had torn out his hair after being left overnight in a sweltering room.

The American Civil Liberties Union obtained the documents under court order through a freedom of information request and publicly released them.

The United States holds about 500 men it suspects of Al Qaeda links at Guantanamo, most of them captured during the Afghanistan war that followed the September 11, 2001, attacks on America.

The Bush administration does not consider them prisoners of war, who would be protected under the Geneva Conventions from torture and coercive interrogation.

Several former prisoners have said they were beaten, threatened with dogs and subjected to freezing temperatures, and the International Committee of the Red Cross has said their treatment was "tantamount to torture".

Military officials at Guantanamo have repeatedly denied the claims, but both SouthCom and the Justice Departments launched investigations after the disclosure of the FBI documents.

A US federal judge yesterday ruled that military tribunals for detainees at the Guantanamo Bay were unconstitutional, leaving in doubt the fate of hundreds of detainees at the US-run detention centre in Cuba.

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