The US Defence Secretary, Robert Gates, has said that Congress should look for ways to close the Guantanamo Bay military prison in Cuba.
Mr Gates said the Guantanamo prison had become "tainted"
He said the military trials of terror suspects at the prison lack credibility because they have been tainted by the harsh treatment of detainees.
But he said that some detainees who have vowed to attack the US should never be released from custody.
The US has started the military trials of terror suspects at Guantanamo Bay.
Mr Gates told a House of Representatives committee that "my own view is that because of things that happened earlier at Guantanamo there is a taint about it."
'Hard core detainees'
He said he wanted the Guantanamo prison to be closed and the trials moved to the US "because I felt that no matter how transparent, no matter how open the trials, if they took place in Guantanamo, in the international community they would lack credibility."
Australian David Hicks pleaded guilty on Monday to providing material support for terrorism in the first case under a new law authorising the military trials.
The chief prosecutor for the military tribunals said on Thursday the prosecution will seek a sentence of "substantially less" than 20 years for him, AP news agency reported.
The US has faced international criticism over its continued detention of suspected al-Qaeda and Taleban militants.
About 385 detainees are still held at Guantanamo Bay
About 385 people are being held at Guantanamo Bay. Some of them have been there for years without facing trial.
"The reality is there are people at Guantanamo we would like to turn back to their home countries, and their home countries won't take them," Mr Gates said.
There were about 100 "hard core" prisoners, he said, who should never be released from custody.
"I don't know if the military prison system provides the capacity to keep them, but I know that there are some people down there who if we release them have made very clear they will come back and attack this country."
He said how to move the "hard core" detainees while ensuring they do not have access to a legal system where they might be released was "an area where frankly I think there needs to be some dialogue between the Congress and the administration."