The alleged mastermind of the September 11, 2001 attacks and his four accused co-plotters will be formally charged by a military tribunal on May 5 at Guantanamo Bay, US officials said Tuesday.

Military judge James Pohl has fixed the date for the arraignment hearing on Saturday, May 5, and it will start at 9:00 am local time, the Pentagon said in a statement signed by the judge.

US officials last week cleared the way for a long-awaited trial of self-confessed 9/11 mastermind Khalid Sheikh Mohammed and his alleged co-conspirators unveiling charges that carry a possible death sentence.

The five are accused of planning and executing the attacks against New York and Washington as well as the downing of a hijacked airplane in a field in Shanksville, Pennsylvania, which killed 2,976 people.

Lawyers for the five could still ask for the hearing to be delayed.

"At the 5 May 2012 session, I will establish a full schedule for the litigation of this case," Pohl said in the statement, published on the website of the military commission.

"Prior to the session, counsel should discuss scheduling and endeavour to agree upon a schedule that works as well as possible for all parties."

Mohammed and his accused conspirators have been held for years at the US-run prison in Guantanamo Bay, Cuba, while a legal and political battle has played out over how and where to prosecute them.

The 46-year-old Mohammed, along with Walid bin Attash of Saudi Arabia, Yemen's Ramzi Binalshibh, Pakistan's Ali Abd al-Aziz Ali -- also known as Ammar al-Baluchi -- and Mustapha Ahmed al-Hawsawi of Saudi Arabia will appear in court for arraignment proceedings.

Their joint trial, which is still months away, will also be held at the American naval base in Guantanamo Bay, where the US government has set up special military commissions to try terror suspects.

Mohammed, who US officials refer to simply as "KSM," has been at the center of a years-old debate over the legal fate of the accused plotters.

After he was captured nine years ago, Mohammed was subjected repeatedly to the simulated drowning technique known as waterboarding that has been widely condemned as torture and other harsh interrogation methods.

His treatment in US custody has raised questions about whether his statements to interrogators will hold up in a trial, but testimony from a former aide may resolve that problem.

Majid Khan, once Mohammed's deputy, has accepted a plea deal with US authorities that will require him to testify against other terror suspects.

After taking office in 2009, Obama initially sought to try Mohammed and his four accused accomplices in a civilian court in New York, just steps from the Ground Zero site where the World Trade Center's twin towers fell in 2001.

But the proposal sparked criticism and the president's Republican foes in Congress put an end to those plans by blocking the transfer of terror suspects to the United States.