U.S. officials rejected the draft report, saying the experts who wrote it made many errors and treated statements from detainees' lawyers as fact. The United States had invited the experts to Guantanamo but would not let them interview detainees, so they refused to go.
The report recommended the United States close Guantanamo Bay and revoke all special interrogation techniques authorized by the Department of Defense. Its experts accused the United States of violating the detainees' rights to a fair trial, freedom of religion and health.
"In their view, the legal regime applied to these detainees seriously undermines the rule of law and a number of fundamental universally recognized human rights, which are the essence of democratic societies," the report said.
The report's findings were based on interviews with former detainees, public documents, media reports, lawyers, and a questionnaire filled out by U.S. officials.
Many of the allegations have been made before, but the document is the first such accounting from the U.N. rapporteurs, who are charged by the U.N. Commission on Human Rights to investigate rights concerns around the world.
The draft was delivered to the United States on Jan. 16, and was first disclosed Sunday by the Los Angeles Times. A final version, which is likely to incorporate U.S. comments, was expected to be released later in the week.
U.S. State Department spokesman Sean McCormack said the United States would not address many of the claims until the final report is released, but defended U.S. practices generally. He focused his remarks on the fact that the experts had refused to go to Guantanamo but wrote the report anyway.
"When people hear these press reports about these outcomes and when they actually view the final report, I would urge them to look at it in the context of the fact that nobody who wrote this report actually went to Guantanamo," McCormack told reporters in Washington. "You shouldn't be writing this kind of report based on assertions by individuals without having ever been there."
The five experts sought invitations from the United States to visit Guantanamo Bay since 2002 and three were offered a visit last year. But they refused in November when they were told they would not be allowed to interview detainees.
The United States believes the International Committee of the Red Cross is the body that should handle that duty. However, ICRC reports are generally kept confidential, while the U.N. experts almost always make their findings public.
"Fact-finding on the spot has to include interviews with detainees," said Manfred Nowak, the U.N. special investigator on torture and one of the experts. "What's the sense of going to a detention facility and doing fact-finding when you can't speak to the detainees? It's just nonsense."
The five U.N. experts have mandates that cover torture, freedom of religion, health, independent judiciary and arbitrary detention. They started working together in June 2004 to monitor conditions at Guantanamo Bay.
They were appointed to their three-year terms by the 53-nation U.N. Human Rights Commission, the global body's top rights watchdog. The commission has come under criticism because its members include countries with poor human rights records such as Cuba and Zimbabwe, but the experts act independently of the body.
While focusing on individual complaints, the report also constituted a larger rebuttal of U.S. policy in Guantanamo. The experts dismissed U.S. claims that the war on terror constitutes an armed conflict, and said they would not classify the detainees as "enemy combatants."
About 500 people are being held in Guantanamo on suspicion of links to al Qaeda or Afghanistan's ousted Taliban government and charges have been filed against approximately 10 detainees.
The report said the U.S. system of justice for the detainees was unfair and cited poor treatment that included prolonged solitary confinement and sensory deprivation. The experts accused doctors of force-feeding detainees on hunger strike in violation of the U.N. Principles of Medical Ethics and standards adopted by the World Medical Association.
Last week, a Kuwaiti prisoner's lawyer released notes alleging aggressive U.S. military tactics meant to end a hunger strike, including strapping detainees into a restraining chair and denying them throat lozenges to ease the pain of the feeding tubes.
McCormack and other U.S. officials said the U.S. treatment did not violate standard practice.
"I have to tell you that the doctors down there comply with accepted international practice when it comes to these questions," McCormack said. "And this is done by medical professionals in a humane way, according to international practice, when there are those individuals who seek to do harm to themselves by going on hunger strike."