A U.N. investigation has concluded that the United States committed acts amounting to torture at Guantanamo Bay, including force-feeding detainees and subjecting them to prolonged solitary confinement, according to a draft report obtained Monday.

U.S. officials rejected the report, saying it was riddled with errors and treated statements from detainees' lawyers as fact.

The report from five U.N. human rights experts also recommended the United States close Guantanamo Bay and revoke all special interrogation techniques authorized by the Department of Defense.

It accused the United States of violating the detainees' rights to a fair trial, to freedom of religion and to health.

"The apparent attempts by the U.S. administration to reinterpret certain interrogation techniques as not reaching the threshold of torture in the framework of the struggle against terrorism are of utmost concern," the draft report said.

The draft report, which follows repeated claims by prisoners at Guantanamo Bay that they have been mistreated or denied their rights, was delivered to the United States on Jan. 16. It was first disclosed Sunday by the Los Angeles Times.

American officials said the most significant flaw of the report was that it judged U.S. treatment of detainees according to peacetime human rights laws. The United States contends it is in a state of conflict and should be judged according to the laws of war.

"Once you fail to even acknowledge that as the legal basis for what we're doing, much of the legal analysis that follows just doesn't hold," a State Department official said.

The official spoke on condition of anonymity because the United States has not formulated an official public response to the draft.

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.

About 500 people are being held in Guantanamo on suspicion of links to al-Qaida or Afghanistan's ousted Taliban government and charges have been filed against 10 detainees.

The draft report, which will be presented to the next session of the human rights commission, dismissed the U.S. claim that the war on terror constitutes an armed conflict. It also said that the detainees at Guantanamo had a right to challenge their detention, and that right was being violated.

"In the case of the Guantanamo Bay detainees the U.S. executive operates as judge, as prosecutor, and as defense counsel," the report said. "This constitutes serious violations of various guarantees of the right to a fair trial before an independent trial."

Manfred Nowak, the U.N. special investigator on torture and one of the five experts, said the report was a draft and had not incorporated U.S. comments. It was expected to be made public later in the week.

"It is a preliminary version," Nowak said, refusing to comment on its substance. "This is an unauthorized preliminary report which might be changed."

U.S. officials faulted the experts for rejecting an invitation to visit Guantanamo Bay, saying it fundamentally undermined the accuracy of their findings.

"The U.N. rapporteurs were invited to visit Guantanamo Bay and they chose not to," said Richard Grenell, spokesman for the U.S. mission to the United Nations in New York. "Had they visited, they would have found that there is no torture going on."

The five experts had sought invitations from the United States to visit Guantanamo Bay since 2002 and accepted the offer in December. But they reversed that decision when they were told they would not be allowed to interview detainees.

"Fact-finding on the spot has to include interviews with detainees," Nowak said. "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."