The US government has rebuffed UK calls to close its controversial detention centre at Guantanamo Bay in Cuba.
Human rights groups have criticised the camp since it opened in 2002
The UK foreign minister said it was unacceptable on human rights grounds and ineffective in fighting terrorism.
But a US spokesman said the camp was needed to house "some very dangerous people", including those who were behind the 9/11 attacks.
Meanwhile fresh allegations of abuse of inmates by US prison guards at the camp have emerged.
Marine Sgt Heather Cerveny, who went to the base three weeks ago as a legal aide to a military lawyer, said five navy guards described in detail how they beat up detainees.
"The one sailor specifically said 'I took the detainee by the head and smashed his head into the cell door'," she said in an affidavit.
The BBC's James Westhead, in Washington, says the allegations are significant because they come from a serving member of the US military.
Sgt Cerveny has reported the matter to the military's inspector general, who is looking in to setting up a formal inquiry.
US State Department spokesman Sean McCormack brushed off calls for Guantanamo to close, saying it would remain open as long as required.
"Look, we don't want Guantanamo open forever. We don't want to be the world's jailers. We certainly would look forward to the day when Guantanamo is closed," he said.
Last month, US Congress passed a bill to allow special military tribunals to prosecute Guantanamo detainees after the Supreme Court blocked the administration's proposals to deal with the inmates.
The UK's Foreign Minister, Margaret Beckett, is the highest ranking British official to publicly criticise the US for its detention of suspects without trial at the camp.
Mrs Beckett said the US detention camp did as much to radicalise extremists as it did to promote security.
"The continuing detention without fair trial of prisoners is unacceptable in terms of human rights, but it is also ineffective in terms of counter-terrorism."
Separately, the Red Cross said on Friday that it had met top terror suspects held at the camp.
The US has said it recently transferred the alleged mastermind of the 9/11 attacks, Khalid Sheikh Mohammed, and other al-Qaeda suspects to the camp.
They were believed to have been held before that in secret CIA-run jails.
Some 450 terror suspects are thought to be detained at the camp.