The CIA has admitted destroying video tapes showing what is described as the "harsh interrogation" of al-Qaeda suspects.
The interrogations of two suspects were taped in 2002 and the tapes were destroyed in 2005, after the Abu Ghraib prisoner abuse scandal in Iraq surfaced.
Michael Hayden, the CIA director, told his staff on Thursday that the tapes were destroyed so identities of interrogators would not be compromised.
Scrutiny and scandal
Hayden said congressional intelligence committee leaders were informed of the existence of the tapes and the CIA's intention to destroy them.
He said the agency's internal watchdog had watched the tapes in 2003 and verified that the interrogation practices recorded were legal.
But Marwan Bishara, Al Jazeera's senior political analyst, said the methods were actually torture and the fact that the CIA had the tapes but did not surrender them when a US commission to look into the 9/11 attacks and congress asked for such information, raised questions about whether the CIA obstructed justice.
The destruction of the tapes comes amid scrutiny over the CIA's "rendition" programme, where suspects were allegedly detained and interrogated in secret locations outside the US.
Amnesty International on Firday called for the destruction of the tapes to be part of that inquiry.
The rights group said in a press release that "the destruction of the tapes falls into a pattern of measures taken by the government that block accountability for human rights violations".
Speaking to Al Jazeera, Mark Agrast, of the Centre for American Progress, said: "The timing is very disturbing because they [the tapes] appear to have been destroyed at precisely the time that the Abu Ghraib photographs had come out and the stories of highly coercive interrogation practices were becoming known."
During the Abu Ghraib scandal in 2004, leaked pictures of US forces abusing Iraqi prisoners caused an international outcry.
Members of the US 9/11 commission and congress have expressed surprise that the tapes existed, saying that the CIA repeatedly claimed it did not record the interrogation of detainees.
Agrast told Al Jazeera: "There will be congressional investigations, because this story was not shared with the house and senate intelligence committees that by law are supposed to be informed of activities of this kind."
Hayden's revelation appeared to be an attempt to pre-empt the New York Times, which informed the CIA on Wednesday evening that it planned to publish a story about the destruction of the tapes.
Hayden said he was informing staff because the press had learnt about the destruction of the tapes.
Protesters outside the US justice department
re-enacted waterboarding in November [EPA]
Hayden's revelation comes a day after the US congress agreed to ban techniques such as waterboarding – where a detainee undergoes similar conditions as drowning – a method of interrogation believed to be filmed on the tapes.
He said the CIA began taping the interrogations as an internal check on the programme after George Bush, the US president, authorised the use of harsh questioning methods.
The methods included waterboarding, government officials said.
"The agency was determined that it proceed in accord with established legal and policy guidelines. So, on its own, CIA began to videotape interrogations," Hayden said in a written message to CIA employees.
The CIA - headed at the time by Porter Goss - also decided to destroy the tapes in "the absence of any legal or internal reason to keep them", Hayden wrote, adding that videotaping of the interrogations stopped in 2002.
"The tapes posed a serious security risk. Were they ever to leak, they would permit identification of your CIA colleagues who had served in the programme, exposing them and their families to retaliation from al-Qaeda and its sympathisers," Hayden's message said.
The CIA says it only taped the interrogation of the first two suspects it held, one of whom was Abu Zubaydah, who told CIA interrogators about alleged September 11 accomplice Ramzi bin al-Shibh, Bush said in 2006.
Al-Shibh was captured and interrogated and, together with Zubaydah's information, he led to the 2003 capture of Khalid Sheikh Muhammad, the suspected al-Qaeda operative held at Guantanamo who has claimed to be behind the September 11, 2001, attacks in the US.
Meanwhile, witness testimony has been heard for the first time since the US began prosecuting Guantanamo suspects.
A US major testified that Salim Ahmed Hamdan, a former driver for Osama bin Laden, was driving a car that contained two small rockets when he was arrested in Afghanistan in 2001.
The hearing will determine whether Hamdan, who says he is not an al-Qaeda member or fighter, an "unlawful enemy combatant" who should be tried before a military tribunal.