Khalid Sheikh Mohammed, accused of masterminding the September 11 attacks, is tentatively due to appear before a U.S. war court judge at Guantanamo Bay for the first time on June 5, a military official said on Wednesday.

The chief judge for the Guantanamo tribunals, Marine Col. Ralph Kohlmann, notified military defence lawyers of the tentative arraignment date for Mohammed and four other captives who could face execution if convicted of murder and conspiracy charges stemming from the 2001 attacks on the United States.

"The judge made it clear that if there were problems with scheduling that he requested to be notified immediately," Army Col. Steve David, the chief defence counsel for the tribunals, said via e-mail.

The American Civil Liberties Union said it was outraged the arraignment was scheduled before the detainees had met with their lawyers. It also accused the U.S. government of delaying security clearances for two civilian attorneys who have offered to represent Mohammed.

"It is extremely disturbing, though not surprising, that the government is brazenly disregarding the rights of the accused without any consideration for due process," said ACLU Executive Director Anthony Romero. "This approach will only add to the illegitimacy of the military commissions."

The Pentagon announced on Tuesday that Susan Crawford, the official overseeing the special court at the U.S. naval base in Cuba, had endorsed the charges against Mohammed and four other prisoners -- Ali Abdul Aziz Ali, Ramzi Binalshibh, Mustafa Ahmed al-Hawsawi and Walid bin Attash.

They are accused of conspiring with al Qaeda to murder civilians and with 2,973 counts of murder, one for each person killed when hijacked passenger planes crashed into the World Trade Center, the Pentagon and a Pennsylvania field.

MANY HURDLES

Crawford's approval cleared the way for their arraignment within 30 days, but the trials still face numerous hurdles.

The CIA has admitted subjecting Mohammed to harsh interrogation methods, including the simulated drowning technique known as waterboarding. That calls into question the reliability of his confession that he planned every aspect of the September 11 attacks.

The former chief prosecutor of the tribunals testified last month that political appointees and higher-ranking officers exerted illegal influence over the process, pushing prosecutors to use coerced evidence and rushing them to file charges against Mohammed and the other "high-value" prisoners before the upcoming U.S. presidential election in November.

A military judge has already disqualified the tribunals' legal adviser, Air Force Brig. Gen. Thomas Hartmann, from further involvement in the pending case against Osama bin Laden's driver, Salim Hamdan, and questioned his ability to act with the impartiality mandated by law.

Defence lawyers are expected to challenge Hartmann's role in the charges against Mohammed and the other four.

The Guantanamo tribunals are the first U.S. war crimes tribunals since World War Two. They were established after September 11 to try non-American captives whom the Bush administration considers "enemy combatants" not entitled to the legal protections granted to soldiers and civilians.