The alleged mastermind of the 9/11 attacks has admitted his role in them, and 30 other plots in a hearing at Guantanamo Bay, the Pentagon says.
"I was responsible for the 9/11 operation, from A to Z,” said Khalid Sheikh Mohammed in a partial transcript from a closed-door hearing.
He also said he had planned attacks on Big Ben and Heathrow airport in London.
The hearing was held to determine whether he was an “enemy combatant”, which could lead to a military trial.
Any criminal charges that are brought could eventually lead to a military tribunal at Guantanamo Bay, Cuba.
“I was the operational director for Sheikh Osama Bin Laden for the organising, planning, follow-up and execution of the 9/11 operation,” Mr Mohammed told the hearing, in a statement read by a representative.
According to the partial transcripts, he also admitted responsibility for a series of attacks, including the 1993 bombing of the World Trade Center in New York, the bombing of nightclubs in Bali in 2002 and a Kenyan hotel in the same year.
He claimed responsibility for the failed attempt by the so-called shoe bomber, Richard Reid, to bring down an American plane.
He also listed a string of plots that never came to fruition, including plans to attack Heathrow Airport, Canary Wharf and Big Ben in London, to hit targets in Israel, and to blow up the Panama Canal.
There was a follow-up project to the 11 September attacks, which involved hitting towers in the US cities of Los Angeles, Seattle, Chicago and the Empire State Building in New York, and to attack US nuclear power stations.
He also claimed to be behind plots to assassinate the late Pope John Paul II and former US President Bill Clinton, the transcript said.
He mentioned the killing in Pakistan of kidnapped US journalist Daniel Pearl - which he has been accused of carrying out personally - but it is not clear whether he was admitting responsibility.
According to the Associated Press news agency, Mr Mohammed confessed to the beheading in a blacked-out section of the transcript.
Mr Mohammed seemed to express some regret over the deaths on 11 September, 2001.
“When I said I"m not happy that 3,000 been killed in America, I feel sorry even. I don't like to kill children and the kids,” he said, according to the transcript.
Transcripts of his testimony were translated from Arabic and edited by the US defence department to remove sensitive intelligence material before release.
It appeared, from a judge's question, that Mr Mohammed had made allegations of torture in US custody.
However, when asked whether his statement was produced under duress, he said it was not.
Mr Mohammed is the most high-profile of 14 “high value” detainees transferred in September from secret CIA prisons abroad to the Guantanamo Bay camp.
Some of the 14 have now appeared in the closed-door hearings, which began over the weekend. Others have refused to take part in the process.
Transcripts have also been released for hearings concerning senior al-Qaeda suspects Abu Faraj al-Libbi and Ramzi Binalshibh, though they both refused to take part in the proceedings.
It is the first time Mr Mohammed has faced a court since his capture in March 2003 in Pakistan.
The US hearings have been widely criticised by lawyers and human rights groups as sham tribunals, with no chance for the defendants to get a fair trial.
Kenneth Roth, executive director of Human Rights Watch, said there was no way of knowing whether the confession was the result of torture.
“We need to know if this purported confession would be enough to convict him at a fair trial,” he said.
Mr Mohammed was said to be the third most senior al-Qaeda leader before his capture.
He has long been seen as the mastermind of the 9/11 plot, the man who went to Osama Bin Laden and suggested the idea of flying planes into buildings.
But his confession of involvement in a wide range of ambitious plots reflects his boastful nature and a desire to portray himself as a terrorist mastermind, says the BBC's security correspondent Gordon Corera.
And while he has admitted his role in such attacks before, the significance of the transcript lies in the fact that he made the statements at the hearing, which could now lead to a trial before a military tribunal, our correspondent says.