PROSECUTORS have filed charges against 9/11 mastermind Khalid Sheikh Mohammed and four alleged co-conspirators, bringing the five a step closer to facing a Guantanamo military tribunal.

The charges, which must now be approved by a tribunal official, set the stage for the highest-profile al-Qaeda suspects in custody to finally face justice almost a decade after the attacks, which killed nearly 3000 people.

"The prosecutors have recommended that the charges against all five of the accused be referred as capital," a Pentagon statement said, meaning the suspects could face the death penalty if convicted.

President Barack Obama's administration last month abandoned plans to try the five in a civilian court just blocks from the twin towers of the World Trade Center in New York, felled by al-Qaeda hijackers on September 11, 2001.

The charges are 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, hijacking aircraft and terrorism.

Almost identical charges were filed in May 2008 but dropped when the Obama administration announced plans to try Sheikh Mohammed, Walid bin Attash, Ramzi Binalshibh, Ali Abd al-Aziz Ali, and Mustapha Ahmed al-Hawsawi in New York.

Retired Navy Vice Admiral Bruce MacDonald, who is the military tribunal's Convening Authority (CA), will consider the latest charges and decide whether or not the death penalty can be sought.

"After this review, the CA - in his sole discretion - may then refer the charges to a military commission," said a letter sent to the families of the 9/11 victims by the Office of Military Commission.

"If referred (capital or non-capital), a military judge would then be assigned and a panel of eligible military officers would be selected as potential members of the military commission. The accused would then be arraigned within 30 days of the service of the referred charge."

Referred to in counter-terrorism circles as "KSM", Sheikh Mohammed, a Kuwaiti-born Pakistani who is now 46 or 47 years old, is the self-proclaimed architect of the September 11 attacks and a host of other anti-Western plots.

He was subjected to simulated drowning, known as waterboarding, 183 times during his years in US custody, and his trial will raise questions about evidence obtained from harsh interrogation methods.

In addition to felling the twin towers, he claims to have personally beheaded US journalist Daniel Pearl in 2002 with his "blessed right hand" and to have helped in the 1993 World Trade Center bombing that killed six people.

Binalshibh is accused of serving as the primary link between the hijackers and al-Qaeda leaders in Afghanistan and Pakistan during the eight months before the attacks.

Abd al-Aziz Ali, a Pakistani raised in Kuwait who is Sheikh Mohammed's nephew, is believed to have transferred funds to US-based operatives and helped hijackers travel from Pakistan to the United States.

In addition to his alleged 9/11 involvement, bin Attash, born and raised in Saudi Arabia to Yemeni parents, is accused of being the mastermind of the 2000 attack on the USS Cole destroyer in Yemen, which killed 17 US soldiers.

Hawsawi is a Saudi associate of al-Qaeda leader Osama bin Laden, who was killed on May 2 in his Pakistani hideout by a US Navy SEAL team. Hawsawi is accused of holding the group's purse strings and of arranging the funding for the September 11 attacks.

The KSM trial has become a huge political football in the United States.

Republican gripes at Obama for his U-turn on a military tribunal will intensify now that essentially the same charges have been filed more than three years later.

The Obama administration argues that it has reformed the military tribunals to give greater protections to defendants and ensure that statements obtained by brutal interrogation are no longer admitted.

In announcing the U-turn in April, Attorney General Eric Holder also said he still felt a civilian courtroom was the best forum and regretted that a military tribunal was now the only way to go because of blanket Republican opposition in Congress.

Human rights groups expressed renewed anger today that the Obama administration was continuing down the wrong path towards a military tribunal they still see as flawed.

"The correct place to try terrorism suspects remains the federal court system, and the Obama administration should have stuck to its original decision to hold fair trials in American courts," said Hina Shamsi, director of the American Civil Liberties' Union National Security Project.