The self-proclaimed mastermind of the September 11 attacks and his four co-defendants are due back in Guantanamo court Monday for hearings to pave the way to their trial.

It will mark the second appearance for Khalid Sheikh Mohammed and the other alleged co-plotters before the special tribunal known as military commissions on the US naval base. They face the death penalty if convicted for the 2001 attacks on the United States that left nearly 3,000 people dead.

With prosecutors refusing to reveal information deemed classified and holding parts of the debates behind closed doors, the American Civil Liberties Union (ACLU) rights group and 14 media groups are calling for complete transparency.

At issue are the torture and abuse the five men said they suffered at the hands of US authorities, and the classified status that President Barack Obama's administration says covers details of the suspects' treatment, citing national security concerns.

Among the petitions that will be examined during the five days of hearings are government motions to "protect against disclosure of national security information" and to "protect unclassified discovery material where disclosure would be detrimental to the public interest."

"If this is going to be a trial about what happened on 9/11... only the truth should come out and not the US government's spin on the truth until they opened the process; right now, it's just their spin," said Cheryl Bormann, who is defending Walid bin Attash of Yemen.

"The government shouldn't be able to hide behind classification issues."

Prior to their 2006 transfer to Guantanamo, the five men, were held at the CIA's secret prisons, where they were subjected to treatment that critics label as torture.

"The public has the right to see the proceedings," said James Connell, who is representing Mohammed's Pakistani nephew Ali Abd al-Aziz Ali, also known as Ammar al-Baluchi.

The ACLU and media groups petitioning the court are protesting a 40-second audio delay for journalists and a select number of members of the public following the proceedings from behind soundproof glass.

They say the delay, which allows a military censor to blur statements whose content is deemed a threat to national security, violates speech and press freedoms enshrined in the First Amendment of the US Constitution.

Lawyers for the accused are also denouncing what they call censorship of all documents and other communication they share with their clients.

Facing a total of 25 appeals, Judge Colonel James Pohl must also rule on whether the defendants can leave the courtroom during debates or choose the clothing they wear to court.