UN human rights investigators have called for the immediate closure of the US detention camp at Guantanamo Bay.
Some inmates have been at the detention camp since 2002
A UN report on conditions in the Cuba camp says the US should try all inmates or free them "without further delay".
Some aspects of the treatment of the 500-strong camp population amount to torture, the UN team alleges.
The US has rejected the closure call, with White House spokesman Scott McClellan saying that the facility houses "dangerous terrorists".
US officials have dismissed most of the allegations as "largely without merit", saying the five investigators never actually visited Guantanamo Bay.
One of the five investigators responsible for the report, UN special rapporteur on torture Manfred Nowak, said the detention of inmates for years without charge amounted to arbitrary detention.
"Those persons either have to be released immediately or they should be brought to a proper and competent court and tried for the offences they are charged with," he told the BBC.
In London, UN High Commissioner for Human Rights Louise Arbour said she could not endorse every recommendation made by the report - but that she could see little alternative to closing down the camp.
Jan 2002: First "illegal combatants" arrive at Camp X-ray. Transferred to Camp Delta in April
Feb 2002: More than 100 out of nearly 600 detainees stage first of many hunger strikes
Oct 2002: First releases include four men returned to Afghanistan and Pakistan
Feb 2004: US officials announce the first charges against two detainees
Mar-May 2004: Dozens of detainees released
July 2004: First military tribunal
Jan 2005: US announces investigation into allegations of abuse
May 2005: US magazine report - later retracted - alleges copies of the Koran mishandled by guards, sparking worldwide protests. US later confirms five cases of mishandling
The report says the US treatment of detainees, some of whom have been held for more than four years, violates their rights to physical and mental health.
The report expresses concern at the use of excessive force during transportation and force-feeding through nasal tubes during hunger strikes, which it says amounts to torture.
The lack of any US investigation into these allegations is a breach of the UN Convention against Torture, it adds.
The report ends by demanding that the UN be granted full and unrestricted access to the camp's facilities, including private interviews with detainees.
The US invited the UN to the camp last year after years of requests, but refused to grant the investigators the right to speak to detainees in private.
The UN said private interviews were a "totally non-negotiable pre-condition" for conducting the visit and refused to send investigators.
The Pentagon has said only the International Committee of the Red Cross needs free access to prisoners.
The charity has been granted access, but reports its findings only to the detaining authorities.
A draft version of the UN document was leaked earlier this week.
The report is based on interviews with former detainees and lawyers acting on behalf of inmates, media reports, reports by non-governmental organisations and US government answers to a questionnaire.