GUANTANAMO BAY NAVAL BASE, CUBA (AFP) - The five men accused of plotting the Sept 11, 2001 attacks - including the alleged mastermind - are this week due back in US military court, though their prospects for an actual trial remain elusive.

More than 14 years after Al-Qaeda hijackers seized four passenger jets and killed about 3,000 people in New York, at the Pentagon and in Pennsylvania, the "9/11 Five" who allegedly helped hatch the plot remain holed up in the US military's prison at Guantanamo Bay in south-eastern Cuba.

Their case is moving at a snail's pace, slowed by numerous defence motions and allegations of government misconduct, coupled with the logistical headache of flying the judge, lawyers and other staff into and out of the US naval base every time the men appear in court.

At the centre of the case is Pakistan-born Khalid Sheikh Mohammed, who was arrested there in 2003 and subjected to "enhanced interrogation" by the Central Intelligence Agency, including numerous waterboarding sessions and "rectal rehydration". He was transferred to Guantanamo in 2006 and has publicly admitted to being the principal planner behind the 9/11 attacks.

All five defendants face the death penalty, but any verdicts are likely years away. This week's proceedings are all pre-trial hearings, with Monday's (Dec 7) session to be closed between lawyers and the judge.

The judge, Colonel James Pohl, will try to sift through a slew of defence motions, including one seeking to depose a former CIA interpreter who was working on one of the defence teams.

Further complicating matters is a workplace dispute, in which women prison guards complained after Col Pohl ordered them to stop escorting the detainees.

The defence had argued that Mohammed experienced sexual humiliation while being tortured by the CIA.

"He's a torture victim," Mohammed's lead attorney David Nevin said. "Having to be handled by female guards recapitulates the torture that he experienced."

Col Pohl in January ordered the women guards to stop touching the detainees, prompting outrage from senior defence officials including Pentagon chief Ashton Carter.

Brigadier-General Mark Martins, the lead prosecutor, acknowledged that frustration among relatives of those killed on 9/11 is palpable, but the process is moving as fast as possible.

"That's the system we set up, and it is not driven by a timeline," he told reporters.

"I understand peoples' frustrations. I hear it all the time, I've got to deal with it. I've got to do our duty in the law."

The other four accused are: Walid bin Attash and Ramzi Binalshibh of Yemen, Ali Abd al-Aziz Ali - Mohammed's nephew - and Mustapha al-Hawsawi of Saudi Arabia.

The men cannot currently be taken to the United Statesto stand trial in federal court, so are being prosecuted in so-called military commissions.

In return for recognising Cuban sovereignty as the island fought the Spanish for independence, the United States made Havana sign an open-ended lease in 1903 to create the 117-sq-km military base.

It's about 925km by road from Havana - not that you could drive straight there. Guantanamo Bay remains sealed off from Cuba by razor wire fencing, huge cactuses and landmines.

The Obama administration in 2009 attempted to put the five on trial in New York, but the ensuing outrage meant charges were reinstated in military court.

Obama has been trying to close Guantanamo since taking office in 2009, but Congress has balked at his efforts.

Critics of the prison camp say it serves as a extremist propaganda tool and shows how America lost its moral compass under the George W. Bush administration in the aftermath of 9/11.

"It is worth remembering the pervasive fear in late 2001 and how immediate the threat felt," Senator Dianne Feinstein wrote in a notorious Senate report into CIA torture released only last year. "We expected further attacks against the nation."

Though the government maintains detainees are held humanely, defence lawyers argue the Kafkaesque nature of indefinite detention is itself unfairly cruel.

"The idea of holding someone for that many years with no idea of whether they'll be free again, not putting them on trial, not imposing a sentence, is something that is a form of torture," said attorney Jonathan Hafetz, who has helped litigate for Guantanamo detainees and co-written a book on the prison.

Brigadier-General Martins disagrees with the assertion.

"That's not what the law says," the general said. "The restraint on freedom is nothing I will ever trivialise but it's not punishment. Purpose matters, and the law matters on these things."

Mr Richard Kammen, who has a client in another Guantanamo case, said that as a "knowledgeable but outside observer", he thought the 9/11 Five would not be tried this decade.

"The 9/11 case is years away from a trial beginning," he said in a phone interview. "I estimate four, minimum."