WASHINGTON (AFP) - A new batch of internal FBI documents released took renewed aim at hard interrogation practices at a US military prison in Guantanamo Bay, Cuba, prompting the military to order an investigation into FBI allegations of prisoner abuse there.

The American Civil Liberties Union released the latest documents on the eve of Senate confirmation hearings of President George W. Bush's choice for attorney general, Alberto Gonzales, the White House counsel who laid the legal foundation for aggressive interrogations of war-on-terror suspects.

"Mr Gonzales bears much of the responsibility for creating the legal framework and permissive atmosphere that led to the torture and abuse at Guantanamo and elsewhere," said ACLU executive director Anthony Romero in releasing the documents obtained through a Freedom of Information Act suit.

The documents, many of which were heavily redacted, included an account of an interrogation in late 2002 in which an FBI special agent observed a female interrogator caress a shackled prisoner, whisper in his ear and then cause him to grimace in pain.

"SA (redacted) asked what had happened to cause the detainee to grimace up in pain," the document said. "The marine said (redacted) had grabbed the detainees thumbs and bent them backwards and indicated that she also grabbed his genitals."

"The marine also implied that her treatment of that detainee was less harsh than her treatment of others by indicating that he had seen her treatment of other detainees result in detainees curling into a fetal position on the floor and crying in pain," it said.

TJ Harrington, a deputy assistant FBI director, recounted the incident in a July 14 letter to Major General Donald Ryder, the head of the army's criminal investigation command, saying it had been referenced in an May 30, 2003 email to FBI headquarters from an FBI behavioral analysis unit at Guantanamo.

Harrington said that although the incident and two others were raised with Pentagon intelligence and general counsel officials at the time, he had no record they were "communicated to DoD (Department of Defense ) for appropriate action."

The letter cited another incident in October 2002 in which a civilian contractor showed an FBI special agent "an unknown bearded long- haired detainee" in an interrogation room. The detainee's condition was not clear because portions of the letter were redacted.

"SA (redacted) asked Mr. (redacted) whether the detainee had spit at interrogators. Mr. (redacted) laughed and stated that the detainee had been chanting the Koran and would not stop."

Harrington said FBI agents also had observed dogs being used "in an aggressive manner to intimidate" a detainee in September or October 2002, and in November saw a detainee after he had been subjected to intense isolation for over three months.

"By late November, the detainee was evidencing behavior consistent with extreme psychological trauma (talking to non-existent people, reporting hearing voices, crouching in a corner of the cell covered with a sheet for hours on end)," he said.

"It is unknown to the FBI whether such extended isolation was approved by appropriate DoD authorities," he said.

A theme of some of the emails was that the FBI had long opposed the military's harsher interrogation methods.

In the wake of the Abu Ghraib prison scandal last year, Steven McGraw, a senior FBI official, sent an email to all special agents assigned to Guantanamo and asked them to report whether they had observed "aggressive treatment, interrogations or interview techniques on GTMO detainees, which was not consistent with Bureau interview policy/ guidelines."

An August 17 email to Harrington reported that 530 FBI employees who served at Guantanamo in some capacity were notified, and 478 responded.

Of those, 26 said they observed some form of mistreatment although not by FBI personnel.

FBI General Counsel Valerie Caproni determined that only nine warranted a follow up interview. The remaining 17 were deemed to be "appropriate DOD approved interrogation techniques," the email said.

The commander of the US Southern Command, which is responsible for the prison at Guantanamo, on Wednesday ordered an investigation into the FBI allegations of abuse, a spokesman for the command said.

"The Command wants to establish the facts and circumstances surrounding all allegations ... and consider the opinions and recommendations of an independent investigating officer," said Colonel David McWilliams, a spokesman for the US Southern Command (Southcom).

In emailed responses to McGraw, some FBI agents assigned to Guantanamo reported seeing the use of strobe lights, loud music and growling dogs during interrogations. Many other emails released were redacted almost in their entirety.

In an earlier batch of emails released last month, an FBI agent reported seeing detainees shackled hand and foot in a fetal position for 18 to 24 hours at a time, and that most had urinated or defecated on themselves. One had "apparently been literally pulling his hair out throughout the night."