More than a dozen independent UN rights experts voiced outrage that the military prison in Cuba created after the September 2001 attacks to house detainees in the US "war on terror" was still operating.

On the 20th anniversary of the first arrivals at the detention centre, they described it as a site of "unparallelled notoriety" and a "stain" on Washington's stated commitment to the rule of law.

"Twenty years of practising arbitrary detention without trial accompanied by torture or ill treatment is simply unacceptable for any government, particularly a government which has a stated claim to protecting human rights," they said in a statement.

Two UN working groups, on enforced disappearance and arbitrary detention, and five independent rights experts called on the US government to close the site, return detainees home or to safe third countries, and to provide remedy and reparation for their torture and arbitrary detention.

As a newly-appointed member of the UN Human Rights Council, it is particularly important for the United States to "close this ugly chapter of unrelenting human rights violations", said the experts, who are appointed by the council, but do not speak on behalf of the UN.

- 'Systematic use of torture' -

"Guantanamo Bay is a site of unparallelled notoriety, defined by the systematic use of torture, and other cruel, inhuman or degrading treatment against hundreds of men brought to the site and deprived of their most fundamental rights," they said.

The experts pointed out that of the some 700 people once detained, 39 men are still being held at Guantanamo, but only nine have ever been charged with or convicted of crimes.

Between 2002 and 2021, nine detainees died in custody -- seven of them reportedly from suicide. None had been charged with a crime, they said.

They insisted that those who had authorised and engaged in torture at Guantanamo should be brought to justice.

"When a state fails to hold accountable those who have authorised and practised torture and other cruel, inhuman or degrading treatment, it sends a signal of complacency and acquiescence to the world," they said.

The experts voiced alarm that military commissions were still undergoing pre-trial proceedings on motions to suppress evidence of torture.

"The continued unfairness of the proceedings," they said, "is a stain on the stated commitment of the United States to the rule of law and constitutional protection."

The experts slammed the US judicial system for failing to protect human rights and uphold the rule of law and thereby "enabling a legal black hole to thrive in Guantanamo."