Alleged al-Qaeda mastermind Khalid Sheikh Mohammed has confessed to the killing of US journalist Daniel Pearl in Pakistan in 2002, the Pentagon says.
Daniel Pearl was kidnapped and his murder shown on the internet
"I decapitated with my blessed right hand the head of the American Jew Daniel Pearl," he is quoted as saying in a revised transcript of US hearing.
Khalid Sheikh Mohammed is being held at Guantanamo Bay, and was questioned by the tribunal there at the weekend.
He also reportedly confessed to plotting 9/11 and many other attacks.
But Amnesty International urged caution in assessing Mr Mohammed's statements, which it said were made without any of the normal legal safeguards.
"Khalid Sheikh Mohammed's 'confession' was not made in a court of law but in a secret screening process that bars lawyers," said Amnesty UK spokesman Mike Blakemore.
"Before his six months at Guantanamo, Khalid Sheikh Mohammed was apparently held in a totally secret CIA-run prison for three-and-a-half years where he alleges torture."
The alleged admission of Pearl's killing had been blacked out in an earlier version of the transcript released by the Pentagon.
The way of the war [is] killing... when you say I'm terrorist, I think it is deceiving peoples
Khalid Sheikh Mohammed
According to US transcript
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Department of Defense spokesman Bryan Whitman said the information was delayed so that Pearl's family could be informed of the news.
Pearl, a reporter for the Wall Street Journal, was kidnapped in Pakistan in 2002. Pictures of his murder appeared on internet sites later, but the identity of the killer was not clear.
British-born Islamist Ahmed Omar Sheikh was sentenced to death for the murder six months later, while three other men were given life imprisonment. They are appealing against the verdict.
Mr Mohammed has long been considered a prime suspect in the case.
"For those who would like to confirm, there are pictures of me on the internet holding his head," he said, according to the Pentagon transcript.
Khalid Sheikh Mohammed appeared at the weekend before a "combatant status review tribunal", designed to assess whether those suspects held at Guantanamo Bay should continue to be held.
In a statement read for him, he said he was "responsible for the 9/11 operation, from A to Z", and also had a role in planning the 2002 Bali bombings and a deadly attack on a Kenyan hotel.
He also listed a string of unfulfilled plots, including attacks on Heathrow airport in London, the Empire State building in New York and the Panama Canal.
The Kuwaiti-born militant was considered al-Qaeda's number three leader until his capture in a safe house in Pakistan in March 2003.
He was held in US custody at an undisclosed location until his transfer to Guantanamo in 2006.