Updated

The Pentagon is investigating new allegations by a civil liberties group that military interrogators at the U.S. prison at Guantanamo Bay (search) posed as FBI agents while using abusive techniques to question detainees.

The American Civil Liberties Union (search) released e-mails that showed FBI officials disapproved of the practice and suggested the military interrogators posed as FBI agents in part to take advantage of the rapport the FBI had established with some detainees at the prison.

The e-mails, obtained under the Freedom of Information Act (search), also describe some harsh interrogation techniques and a suggestion they were approved by President Bush — a charge the White House vigorously denied.

Pentagon spokesman Bryan Whitman said posing as FBI agents is not on a list of interrogation methods approved by Defense Secretary Donald H. Rumsfeld (search).

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. The FBI declined comment.

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.

In one of the e-mails 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.

In one e-mail, 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.

While military interrogators are performing much of the questioning at Guantanamo, the FBI and CIA also have operations there.

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.

In other developments, a military review found a second Guantanamo prisoner wrongly classified as an enemy combatant, and he will be released soon to his home country, Navy Secretary Gordon England said Monday.

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.

Of the roughly 200 detainees already released, at least a dozen have returned to the battlefield. More than 300 additional cases are still being reviewed.

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.