Amnesty International and Reprieve have called on the UK government to urgently intervene to help prevent unnecessary loss of life from the ongoing hunger strike at the US detention centre at Guantanamo Bay, Cuba.

There are at least six UK residents among an estimated 210 of the camp's 500 detainees currently on hunger strike in protest at their continuing detention without charge or trial at the military prison.

Amnesty International and Reprieve have today written to Tony Blair seeking assurances that the government will make an immediate assessment of the number of British residents on hunger strike, ascertain the gravity of their medical condition, and obtain from the US authorities a guarantee that an independent body is given access to all UK residents on hunger strike.

Amnesty International UK Director Kate Allen said:

"Reports emerging from the camp concerning the treatment of hunger strikers are disturbing and just underline the need for an immediate resolution of Guantanamo Bay.

"The camp is still closed to Amnesty International and the secrecy surrounding Guantanamo makes the hunger strike a frightening phenomenon. We just don’t know what is happening, to whom and with what degree of consent?

"While those on hunger strike have made a personal decision it is notable that their demands - for a fair trial and legal representation - are precisely those required under international law. "We need to see the UK government intervening to prevent deaths and injuries and to see that all detainees - including at least six UK residents on hunger strike - are either properly tried or immediately released in accordance with international human rights law.

Reprieve's Legal Director, Clive Stafford Smith, who is acting on behalf of some 40 Guantanamo Bay detainees, said:

"I have been to Guantánamo Bay. Conditions there at the best of times are disturbing. But to imagine my clients being held in four point restraints with a tube forced down their noses, after all that they have been through just makes me sick. All these prisoners are asking for is that the US military abide by the Geneva Conventions.

They are being forced to risk their lives to persuade a rogue nation to comply with international law. I wrote to Jack Straw on September 12, on behalf of the British residents, asking to know what had been done but I have not heard back; meanwhile with each day that passes my clients’ health is deteriorating. We cannot wait any longer."

Earlier today disturbing accounts of force-feeding of hunger strikers at Guantanamo Bay were heard at a press conference held by Amnesty International and Reprieve. These included accounts of force-feeding of prisoners who had been forcibly restrained (photographs of a reconstruction of these alleged techniques are available).

The conference also heard a direct plea to the UK government from Amani Deghayes, the sister of a UK resident Omar Degayes, who is imprisoned at Guantanamo Bay.

• Click Here for Guantanamo Bay information page.

The strike that began on August 8 over conditions and lack of legal rights is the most widespread of a handful of such protests since the prison camp at the US naval base at Guantanamo in Cuba opened in January 2002, the New York-based Centre for Constitutional Rights (CCR) said.

US army Lieutenant Colonel Jeremy Martin, a Guantanamo spokesman, said 26 detainees were taking part in a "voluntary fast", including 22 hospitalised for "involuntary feedings" involving food given through a nasal tube and fluids given intravenously. Some rights activists have criticised this force feeding.

Martin said the number peaked at 131 last month and has since steadily declined. "The detainees are all clinically stable, closely monitored by medical personnel to ensure that they don't harm themselves - and will continue to receive appropriate nutrition, fluids and excellent medical care " Martin added.

Amnesty International rejected Martin's account.

"Even the language that they're using is totally indicative of the fact they re trying to minimise this," said Amnesty International official Jumana Musa

"What is a 'voluntary fast'? This didn't start because of Ramadan (the current Islamic holy month in which Muslims fast). That's a voluntary fast. This is a hunger strike, which is basically people pledging to starve themselves to death."

The International Committee of the Red Cross (ICRC) in Geneva underlined its concern.

"There is a hunger strike, the situation is serious, and we are following it with concern," said ICRC spokeswoman Antonella Notari.

The hunger strike is the latest flash-point between the US government and human rights groups over the camp, which activists call a blight on the US human rights record.

The Centre for Constitutional Rights, along with affiliated lawyers, represents more than 200 of the approximately 505 detainees at Guantanamo.

CCR lawyer Barbara Olshansky said her group estimates about 210 prisoners are taking part in the hunger strike, and accused the military of deliberately understating the strike's scope.

Olshansky acknowledged her group had not been able to perform a systematic head count of participants at the secretive prison, and said the estimate was based on data gathered by lawyers visiting detainees in recent weeks.

Australian terrorist suspect David Hicks is among some 505 detainees being held in the prison. Human rights groups have denounced these indefinite detentions and treatment they say amounts to torture. Most detainees were picked up in Afghanistan after the United States invaded in 2001 to oust the Taliban government and dislodge al-Qaeda bases.

The hunger strike began after the military reneged on promises given to detainees to bring the prison into compliance with the Geneva Conventions, CCR said. Detainees were willing to starve themselves to death to demand humane treatment and a fair hearing on whether they must stay at the prison, it said.

• Click Here for Guantanamo Bay information page.