Khalid Sheikh Mohammed was captured in Pakistan in 2003
The Pentagon has announced charges against six Guantanamo Bay prisoners over their alleged involvement in the 11 September 2001 attacks in the US.
Prosecutors will seek the death penalty for the six, who include alleged plot mastermind Khalid Sheikh Mohammed.
The charges, the first to allege the Guantanamo inmates' direct involvement in 9/11, are expected to be heard by a controversial military tribunal system.
About 3,000 people died in the hijacked plane attacks.
The Guantanamo Bay detention centre, in south-east Cuba, began to receive US military prisoners in January 2002. Hundreds have been released without charge but about 275 remain and the US hopes to try about 80.
Brig Gen Thomas Hartmann, a legal adviser to the head of the Pentagon's Office of Military Commissions, said the charges alleged a "long-term, highly sophisticated plan by al-Qaeda to attack the US".
He said there would be "no secret trials" and that they would be "as completely open as possible".
"Relatively little amounts of evidence will be classified," Gen Hartmann said.
The other five defendants are Ramzi Binalshibh, a Yemeni, Walid Bin Attash, also from Yemen, Ali Abd al-Aziz Ali, who was born in Balochistan, Pakistan, and raised in Kuwait, Mustafa Ahmad al-Hawsawi, a Saudi, and Mohammed al-Qahtani.
Khalid Sheikh Mohammed
Walid Bin Attash (above)
Ali Abd al-Aziz Ali
Mustafa Ahmad al-Hawsawi
Gen Hartmann said the charges included conspiracy, murder in violation of the laws of war, attacking civilians, destruction of property and terrorism.
All but Mr Qahtani and Mr Hawsawi are also charged with hijacking or hazarding an aircraft.
The charges listed "169 overt acts allegedly committed by the defendants in furtherance of the September 11 events".
Gen Hartmann said: "The accused will have his opportunity to have his day in court.
"It's our obligation to move the process forward, to give these people their rights."
He said they would be given military and civilian defence lawyers and would have the right of appeal.
In listing more details of the charges against the defendants, Gen Hartmann alleged that Khalid Sheikh Mohammed had proposed the attacks to al-Qaeda leader Osama Bin Laden in 1996, had obtained funding and overseen the operation and the training of hijackers in Afghanistan and Pakistan.
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Khalid Sheikh Mohammed, a Kuwaiti of Pakistani extraction, was said to have been al-Qaeda's third in command when he was captured in Pakistan in March 2003.
He has reportedly admitted to decapitating kidnapped US journalist Daniel Pearl in 2002 but these charges do not relate to that.
The BBC's Vincent Dowd in Washington says Khalid Sheikh Mohammed has said he planned every part of the 9/11 attacks but that his confession may prove problematic as the CIA admitted using controversial "waterboarding" techniques.
Human rights groups regard the procedure as torture.
US Homeland Security Secretary Michael Chertoff told the BBC the trials would be fair.
Asked if evidence obtained from waterboarding - a controversial interrogation technique that simulates drowning - would be used, he said: "The judges will decide what's reasonably admissible and what's not admissible."
The charges will now be sent to Susan Crawford, the convening authority for the military commissions, to determine whether they will be referred to trial.
Conspiracy, murder in violation of the law of war, attacking civilians, attacking civilian objects, intentionally causing serious bodily injury, destruction of property in violation of the law of war, terrorism and providing material support for terrorism (all six defendants)
Hijacking or hazarding a vessel (four defendants only - Ramzi Binalshibh, Walid Bin Attash, Ali Abd al-Aziz Ali and Khalid Sheikh Mohammed)
Any trials would be held by military tribunal under the terms of the Military Commissions Act, passed by the US Congress in 2006.
The Act set up tribunals to try terror suspects who were not US citizens.
The law is being challenged by two prisoners at Guantanamo Bay, who say they are being deprived of their rights to have their cases heard by a US civilian court.
Responding to the new charges, a representative of Mohammed al-Qahtani said they would create "show trials".
Centre for Constitutional Rights in New York executive director Vincent Warren said: "These trials will be using evidence obtained by torture as a means to convict someone and execute them and that is absolutely abhorrent to what we believe in here in America.''
Nineteen men hijacked four planes in the 9/11 attacks. Two planes hit the World Trade Center in New York, another the Pentagon in Washington and the fourth crashed in Pennsylvania.