Guantanamo Bay should be closed down, Foreign Secretary Margaret Beckett has said during a speech on human rights.
Mrs Beckett said the camp was ineffective in counter-terrorism
The US detention camp did as much to radicalise new extremists as it did to promote security, Mrs Beckett said.
She added: "The continuing detention without fair trial of prisoners is unacceptable in terms of human rights."
Some 450 terror suspects are thought to be detained at the camp in Cuba - criticised for holding inmates without trial and for abuse allegations.
Launching the Foreign Office's ninth annual human rights report, Mrs Beckett said: "As the prime minister has said, we believe that camp should close.
"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.
"It is widely argued now that the existence of the camp is as much a radicalising and destabilising influence as it is a safeguard to security."
Since the camp started taking foreign prisoners in 2002, it has attracted widespread criticism.
Human rights groups have criticised the camp since it opened in 2002
United Nations human rights investigators have called for the camp's closure and Lord Chancellor Lord Falconer has called it a "shocking affront to democracy".
UK Prime Minister Tony Blair has called it an "anomaly".
The US has said it is a matter of security and military necessity in the "war on terror" and said inmates are treated humanely.
Mrs Beckett also disputed a report in the medical journal The Lancet that as many as 655,000 Iraqi civilians had been killed since the war began in 2003.
"No-one disputes that there have been many deaths in Iraq and all of those deaths are regrettable and tragically many have been deaths of civilians," she said.
"That doesn't mean one has to accept every figure that someone comes up with."
She said the British government did not keep official figures for Iraqi civilians, but got information from the Iraqi government and others.
"The [Lancet] report gives a figure which is orders of magnitude different from that which comes from any other source," she said.
US President George Bush said on Wednesday the figure was "not credible" - he has previously put the civilian death toll in Iraq at 30,000.
Mrs Beckett also said human rights abuses in Iraq and Afghanistan were not an indictment of the prime minister's foreign policy.
"In neither of those countries was it the case that human rights abuses were acknowledged or opposed or investigated and dealt with [under the previous regimes].
"It's dreadful that those abuses continue, but they continue at a time when we are trying our utmost to bring them to an end."