Annan said he didn't necessarily agree with everything in the report but he did support its opposition to people being held in perpetuity without being charged and giving a chance to explain themselves in a court.
"I think sooner or later there will be a need to close the Guantanamo, and I think it will be up to the government to decide, and hopefully to do it as soon as is possible," the secretary-general told reporters.
The report, summarizing an investigation by five U.N. experts, called on the U.S. government "to close down the Guantanamo Bay detention center and to refrain from any practice amounting to torture or cruel, inhuman or degrading treatment."
The 54-page report summarizing the probe called on the U.S. government "to close down the Guantanamo Bay detention center and to refrain from any practice amounting to torture or cruel, inhuman or degrading treatment."
But the U.S. ambassador to U.N. offices in Geneva, Kevin Moley, responded that the investigation had taken little account of evidence provided by the United States, and that the five U.N. experts rejected an invitation to visit Guantanamo.
"It is particularly unfortunate that the special rapporteurs rejected the invitation and that their unedited report does not reflect the direct, personal knowledge that this visit would have provided," Moley wrote in a response that was included at the end of the report.
was leaked earlier this week before it included U.S. comment.
The U.S. is holding about 490 men at the U.S. military detention center on the southeastern tip of Cuba. The detainees are accused of having links to Afghanistan's ousted Taliban regime or the al Qaeda terror group, though only a handful have been charged since the mission opened in January 2001.
The White House rejects calls to shut down the prison camp at Guantanamo Bay, reports CBS News correspondent Mark Knoller.
Responding to questions about the UN report, spokesman Scott McClellan said the detainees are treated humanely, the International Red Cross has full access and reporters are encouraged to visit to see for themselves.
He said the detainees are dangerous terrorists and "nothing's changed in terms of our views" about operating the camp.
The five U.N. experts who authored the report had sought invitations from the United States to visit Guantanamo Bay since 2002. Three were invited last year, but refused in November after being told they could not interview detainees.