http://news.bbc.co.uk/2/hi/americas/4113679.stm
Fresh allegations have emerged of serious mistreatment of Iraqi prisoners by US military personnel.
Memos between FBI officials detailing abuses, some dated after the Abu Ghraib jail scandal, were released as part of a lawsuit against the government.
Others allege serious abuse of inmates held at the Guantanamo Bay naval base, mostly captives from the Afghan war.
The American Civil Liberties Union brought the case to determine whether the US was mistreating prisoners.
ACLU executive director Anthony Romero said the documents raised grave questions about who was to blame for widespread detainee abuse.
"Top government officials can no longer hide from public scrutiny by pointing the finger at a few low-ranking soldiers," he said.
Last week documents released for the case threw up fresh revelations of abuse in Iraq by US marines, 13 of whom have been convicted and some jailed.
'Executive order'
The documents, which were obtained through the Freedom of Information Act, are mostly made up of communications between FBI agents concerned at seeing interrogation techniques they are prohibited from using in their own investigations.
One of the memorandums released on Monday provided the account of an agent who observed "serious physical abuses" in Iraq.
It was dated 24 June - two months after the extent of abuse at Baghdad's Abu Ghraib prison was revealed - and was marked "urgent" and sent to FBI Director Robert Mueller.
It described strangulation, beatings and the placing of lit cigarettes into detainees' ears.
Another document said an executive order signed by President George W Bush had authorised techniques such as "sleep management", stress positions, use of military dogs and sensory deprivation.
The White House was quick to respond to this allegation, saying: "What the FBI agent wrote in the e-mail is wrong. There is no executive order on interrogation techniques."
Impersonation
A document relating to Guantanamo suggests that detainees - mostly suspected Taleban and al-Qaeda fighters captured during the war in Afghanistan - were shackled to the floor in foetal positions for more than 24 hours at a time, left without food and water and allowed to defecate on themselves.
One detainee's air conditioning was turned off in an unventilated room, making it unbearably hot, it was reported.
"The detainee was almost unconscious on the floor with a pile of hair next to him," the memo said. "He had apparently been literally pulling his own hair out throughout the night."
Other allegations contained in the e-mails include:
That military interrogators impersonated FBI agents, apparently to avoid possible blame in subsequent inquiries
That this method was approved by Deputy Defence Secretary Paul Wolfowitz
The rape of a juvenile male detainee at Abu Ghraib prison, currently under investigation
That one Guantanamo detainee was wrapped in an Israeli flag and bombarded with loud music in an apparent attempt to soften his resistance to interrogation.
The Pentagon has not commented on the latest allegations of abuse, but spokesman Bryan Whitman denied that Mr Wolfowitz had approved impersonation techniques.
The department has also said in relation to previous cases that it did not tolerate abusive tactics.
Some allegations in the documents are under investigation, the Pentagon added.
Fresh allegations have emerged of serious mistreatment of Iraqi prisoners by US military personnel.
Memos between FBI officials detailing abuses, some dated after the Abu Ghraib jail scandal, were released as part of a lawsuit against the government.
Others allege serious abuse of inmates held at the Guantanamo Bay naval base, mostly captives from the Afghan war.
The American Civil Liberties Union brought the case to determine whether the US was mistreating prisoners.
ACLU executive director Anthony Romero said the documents raised grave questions about who was to blame for widespread detainee abuse.
"Top government officials can no longer hide from public scrutiny by pointing the finger at a few low-ranking soldiers," he said.
Last week documents released for the case threw up fresh revelations of abuse in Iraq by US marines, 13 of whom have been convicted and some jailed.
'Executive order'
The documents, which were obtained through the Freedom of Information Act, are mostly made up of communications between FBI agents concerned at seeing interrogation techniques they are prohibited from using in their own investigations.
One of the memorandums released on Monday provided the account of an agent who observed "serious physical abuses" in Iraq.
It was dated 24 June - two months after the extent of abuse at Baghdad's Abu Ghraib prison was revealed - and was marked "urgent" and sent to FBI Director Robert Mueller.
It described strangulation, beatings and the placing of lit cigarettes into detainees' ears.
Another document said an executive order signed by President George W Bush had authorised techniques such as "sleep management", stress positions, use of military dogs and sensory deprivation.
The White House was quick to respond to this allegation, saying: "What the FBI agent wrote in the e-mail is wrong. There is no executive order on interrogation techniques."
Impersonation
A document relating to Guantanamo suggests that detainees - mostly suspected Taleban and al-Qaeda fighters captured during the war in Afghanistan - were shackled to the floor in foetal positions for more than 24 hours at a time, left without food and water and allowed to defecate on themselves.
One detainee's air conditioning was turned off in an unventilated room, making it unbearably hot, it was reported.
"The detainee was almost unconscious on the floor with a pile of hair next to him," the memo said. "He had apparently been literally pulling his own hair out throughout the night."
Other allegations contained in the e-mails include:
That military interrogators impersonated FBI agents, apparently to avoid possible blame in subsequent inquiries
That this method was approved by Deputy Defence Secretary Paul Wolfowitz
The rape of a juvenile male detainee at Abu Ghraib prison, currently under investigation
That one Guantanamo detainee was wrapped in an Israeli flag and bombarded with loud music in an apparent attempt to soften his resistance to interrogation.
The Pentagon has not commented on the latest allegations of abuse, but spokesman Bryan Whitman denied that Mr Wolfowitz had approved impersonation techniques.
The department has also said in relation to previous cases that it did not tolerate abusive tactics.
Some allegations in the documents are under investigation, the Pentagon added.
