The UN Secretary General, Kofi Annan, has said the United States must shut down Guantanamo Bay prison camp "as soon as is possible".
Only a handful of the approximately 500 detainees have been tried
Mr Annan backed a UN report calling for the closure of the camp where some 500 "enemy combatants" have been held without trial for up to four years.
He said he did not agree with all findings, but said detainees could not be held "in perpetuity" without charge.
The White House has dismissed the report as "a discredit to the UN".
The UN says the US should try the approximately 500 inmates, or free them "without further delay".
Mr Annan said bringing the detainees to trial would allow them to explain themselves.
Only a handful of detainees have been tried so far.
While he did not agree with all the findings of the report, Mr Annan said it was crucial to strike a balance.
"The basic premise, that we need to be careful to have a balance between effective action against terrorism and individual liberties and civil rights, I think is valid," Mr Annan told reporters.
White House spokesman Scott McClellan rejected the call to close the camp.
Mr McClellan said the military treated all detainees humanely. "These are dangerous terrorists that we're talking about," he added.
"They are people that are determined to harm innocent civilians, or harm innocent Americans. They were enemy combatants picked up on the battlefield in the war on terrorism."
A senior British minister also called for the camp to be closed.
Speaking on the BBC television Question Time programme, Peter Hain said he would prefer to see Guantanamo Bay close.
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
He also indicated that the UK Prime Minister, Tony Blair, agreed with him.
The US has dismissed most of the findings of the report which include allegations of torture.
It said most of the allegations were "largely without merit" as the five investigators never actually visited Guantanamo Bay.
The investigators say they rejected an offer to go to Guantanamo, as they would not have been allowed to meet the prisoners.
The report will be presented to the UN Commission of Human Rights, which authorised the report, at its next session in Geneva on 13 March.