In a major about-face, the Obama administration will try Khalid Sheikh Mohammed and four other alleged 9/11 plotters in a military tribunal at Guantanamo rather than a civilian court.

Attorney-General Eric Holder “reluctantly” reversed course on Monday, insisting the accused co-conspirators of the September 11, 2001 attacks could have been successfully prosecuted in federal court.

He blamed Congress for imposing measures blocking the trials of Guantanamo inmates in the United States.

President Barack Obama's administration had to “face a simple truth” that the congressional restrictions were “unlikely to be repealed in the immediate future,” said Mr. Holder.

“And we simply cannot allow a trial to be delayed any longer for the victims of the 9/11 attacks or for their family members who have waited for nearly a decade for justice.”

Mr. Holder formally referred the cases of Sheikh Mohammed, Walid bin Attash, Ramzi Binalshibh, Ali Abd al-Aziz Ali and Mustapha Ahmed al-Hawsawi to the Defence Department for trials before military commissions.

The move came the same day the President announced plans to stand for re-election and also followed a decision earlier on Monday by the U.S. Supreme Court rejecting three appeals by Guantanamo detenus protesting their indefinite detention.

Mr. Obama has vowed to close Guantanamo, having held it up as a “legal black hole” and “recruitment tool for terrorists” that symbolised all that was wrong with the so-called “war on terror” waged by his predecessor, George W. Bush.

But the high-profile trials of Sheikh Mohammed and the four other alleged Al-Qaeda figures planned for the U.S. naval base in south-eastern Cuba suggested Mr. Obama had given up closing the detention centre any time soon.

In one of his first acts as President in 2009, Mr. Obama halted trials at Guantanamo and announced he would close the controversial detention camp within a year.

But he has been thwarted in his ambition by legal complications and mounting opposition from both friends and foes in Congress.

“For the sake of the safety and security of the American people, I'm glad the president reconsidered his position on how and where to try these detainees,” said Mitch McConnell, the Senate Republican leader.

Mr. Obama's position softened last month when he lifted a two-year freeze on new military trials for Guantanamo terror suspects, paving the way for Monday's decision.

Known in counter-terrorism circles as “KSM,” Sheikh Mohammed is the self-proclaimed architect of 9/11 and a host of other anti-Western plots. His trial likely will face questions about evidence obtained from harsh interrogations carried out by U.S. agents, though the military commissions operate under more lenient rules for the prosecution than a civilian court. Sheikh Mohammed is known to have been “waterboarded” or subjected to simulated drowning 183 times during his years in U.S. custody, a method widely recognised as torture.

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