The White House has rejected a UN report demanding the immediate closure of the Guantanamo Bay prison camp calling it "a discredit to the UN".
Some inmates have been at the detention camp since 2002
White House spokesman Scott McClellan said investigators failed to examine the facts and that their time would be better spent studying other cases.
The report says the US should try all approximately 500 inmates, or free them "without further delay".
Aspects of the treatment at the camp amount to torture, the UN team alleges.
In response, UN Secretary General Kofi Annan said that "sooner or later" the camp will have to close, but added that he did not agree with all elements of the latest report.
However, he said he hoped the US government would close the camp "as soon as possible".
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.
The US has dismissed most of the allegations as "largely without merit", saying the five investigators never actually visited Guantanamo Bay and that detainees are treated humanely.
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 United Nations should be making serious investigations across the world, and there are many instances in which they do when it comes to human rights. This was not one of them," Mr McClellan said.
"And I think it's a discredit to the UN when a team like this goes about rushing to report something when they haven't even looked into the facts, all they've done is look at the allegations."
Earlier Mr McClellan described the UN report as "a rehash" of past claims made by lawyers representing the prisoners saying: "We know that al-Qaeda terrorists are trained in trying to disseminate false allegations."
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.
It 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 Pentagon has said only the International Committee of the Red Cross needs free access to prisoners.