The situation at Guantanamo Bay - where dozens of detainees are on hunger strike - is serious, the International Committee of the Red Cross has warned.
The Guantanamo detainees have not been charged
Last month, ICRC officials visited the US camp, where some 500 alleged Taleban and al-Qaeda fighters are being held.
But spokeswoman Antonella Notari said she could not comment on details of what they had witnessed there.
Inmates' lawyers say some 200 men have taken part in the fast which began in August. About 20 are being force-fed.
The US authorities say that only 28 detainees remain on hunger strike, of whom 22 are being fed through tubes at the prison hospital.
A spokesman at the US base in Cuba, Lieutenant Colonel Jeremy Martin, said the men were being closely monitored and were in stable condition.
Clive Stafford Smith, a lawyer for 40 of the detainees, said some of them had been shackled to their beds to stop them removing the feeding tubes.
The ICRC backs a 1975 declaration that states that doctors should not take part in force-feeding.
On Thursday, human rights groups called on the UK government to intervene to resolve the hunger strike.
Amnesty International disputes US figures and says that 210 detainees are currently refusing food, protesting against their detention without trial or charges.
The Pentagon has described the inmates' action as a rolling hunger strike, with groups of them taking turns to refuse food.
Many of the detainees have been held at the camp since it was set up in 2002, after the US-led offensive against the Taleban regime in Afghanistan.