The American Civil Liberties Union released e-mails that showed FBI officials disapproved of the practice and suggested the military interrogators were trying to take advantage of the rapport the FBI had established with some detainees at the prison in Cuba.
The e-mails, obtained under the Freedom of Information Act, also describe some harsh interrogation techniques in Iraq, and suggest they were approved by President Bush.
The White House denied a suggestion in an FBI e-mail dated May 22, 2004, that Bush personally signed off on certain interrogation techniques in an executive order.
A report on torture techniques used in Iraq dated June 25, 2004 and sent to FBI director Robert Mueller warned a witness had seen abuses including "strangulation, beatings, placement of lit cigarettes into the detainees' ear openings and unauthorized interrogations."
The military operation at Guantanamo Bay has come under increased scrutiny as former prisoners have alleged they were tortured. The Pentagon maintains it runs a humane operation there, and says all allegations of abuse are investigated.
The ACLU's latest disclosures primarily constitute e-mails between FBI officials whose names the government removed before releasing them. In several, the writers describe and criticize various interrogation techniques they say they witnessed at Guantanamo.
While military interrogators are performing much of the questioning at Guantanamo, the FBI and CIA also have operations there.
In one, the writer described seeing a "detainee sitting on the floor of the interview room with an Israeli flag draped around him, loud music being played and a strobe light flashing." Another Guantanamo prisoner has, in a court petition, described detainees wrapped in Israeli flags, among other allegations. At the time, a Guantanamo Bay spokesman denied his statements.
In another message, dated from August, the writer reports more than once witnessing prisoners chained to the floor in a fetal position, with no food or water. They had often soiled themselves. On one occasion, the temperature in a room was lowered so much the barefooted detainee shivered. In another, the room was so hot the detainee had pulled out some of his hair before passing out.
Pentagon spokesman Bryan Whitman said posing as FBI agents is not on a list of interrogation methods approved by Defense Secretary Donald Rumsfeld.
Asked about Guantanamo at a news conference Monday, Mr. Bush said, "You've got to understand the dilemma we're in. These are people that got scooped up off a battlefield attempting to kill U.S. troops. And I want to make sure, before they're released, that they don't come back to kill again."
A military review has found a second prisoner wrongly classified as an enemy combatant, and he will be released soon to his home country, the Navy's top civilian said Monday.
Of the roughly 200 detainees already released, at least a dozen have returned to the battlefield, Navy Secretary Gordon England said.
The newest prisoner to face release would be the second freed under a military process instituted after the U.S. Supreme Court ruled last summer that prisoners at Guantanamo could challenge their detentions through the U.S. court system.
To bolster its case for each of the prisoners against any such challenge, the Pentagon set up tribunals to review circumstances of each man's capture to determine whether they are properly held.
England refused to identify the prisoner to be released by name or nationality, and the circumstances of his capture were not immediately available. The State Department has been notified of the decision and will arrange his return home.
More than 300 additional cases are still being reviewed.
Anthony Romero, executive director of the ACLU, say the FBI documents continue to show the U.S. government was "torturing individuals in some instances" and demonstrates a major rift between FBI agents and the military over proper interrogation techniques.
"There was real concern within our law enforcement community about whether we are torturing individuals," Romero said.
The May 22 e-mail suggesting that Mr. Bush personally signed off on harsher techniques drew a swift denial from the White House.
"What the FBI agent wrote in the e-mail is wrong. There is no executive order on interrogation techniques," White House press secretary Scott McClellan said Monday. "Interrogation methods for military detainees are decisions made by the Department of Defense."
The FBI declined to comment.
The e-mail reads: "We are aware that prior to a revision in policy last week, an Executive Order signed by President Bush authorized the following interrogation techniques among others sleep 'management,' use of MWDs (military working dogs), 'stress positions' such as half squats, 'environmental manipulation' such as the use of loud music, sensory deprivation through the use of hoods, etc." The memo continues, "I have been told that all interrogation techniques previously authorized by the Executive Order are still on the table but that certain techniques can only be used if very high-level authority is granted."
Separately Monday, a federal judge in New York said he would deny a government request to delay a review of whether certain CIA internal files related to Iraq should be made public.
Judge Alvin Hellerstein's comments marked a victory for the ACLU and other groups seeking information about the treatment of detainees at Guantanamo and in Iraq.
Also Monday, lawyers said a Navy SEAL was acquitted of charges that he beat a handcuffed and hooded terror suspect who later died, while a second commando received probation for assaulting another prisoner.
The first SEAL, a first-class petty officer, was found not guilty of assault and dereliction of duty Thursday in a nonjudicial proceeding known as a captain's mast, according to his attorney, Jeremiah Sullivan.
The other commando, a second-class petty officer, was convicted Friday of assault and received six months probation, said his attorney, Milt Silverman.
Both hearings, closed to the public, were held before SEAL Capt. James O'Connell at Naval Special Warfare Command in Coronado, outside San Diego.