Image caption President Obama vowed to close Guantanamo Bay in January 2009

An open letter published in the Lancet medical journal calls for hunger-striking Guantanamo Bay detainees to receive independent medical care.

More than 150 doctors and medical professionals signed the letter to US President Barack Obama.

At least 100 prisoners are protesting against their indefinite detention by refusing food.

An earlier letter by 13 detainees said it was impossible to trust military doctors who had helped force-feed them.

The detainees are being held at the US military prison on Cuba which Mr Obama has said he will make a renewed attempt to close.

Lawyers representing some of those on hunger strike say their clients regularly collapse through weakness as the protest takes its toll.

The medical staff is scared because they don't know how to measure the vitals with all the shackling and cannot complain Ahmed Belbacha, Guantanamo detainee

The letter published in the Lancet on Wednesday said the detainees had "very good reason" not to trust US medical doctors, as they are required to follow orders of military commanders.

"Without trust, safe and acceptable medical care of mentally competent patients is impossible," the letter said.

"Since the detainees do not trust their military doctors, they are unlikely to comply with current medical advice.

"That makes it imperative for them to have access to independent medical examination and advice, as they ask, and as required by the UN and World Medical Association."

Ahmed Belbacha, a 43-year-old Algerian who has been held at Guantanamo for the past 11 years, said every day of the hunger strike was "an ordeal".

Speaking to the BBC's Newshour through his lawyer, he said prisoners are shackled as they are force-fed, and strapped into a feeding chair with their hands tied to their stomachs. The process is often made worse by the "inexperience or indifference" of medical staff, and many detainees vomit during or after the process, he said.

"I try to do it when they will not notice - because if they did they would put me in the chair and feed me again.

"The medical staff is scared because they don't know how to measure the vitals with all the shackling and cannot complain," he said.

"I tell the doctors that force feeding me is a violation of their medical ethics, but they say that the order comes from the guards and they have no control."

'Koran mishandled'

The current hunger strike, which began in February, is the longest in the military prison's history. Lawyers representing detainees say it was sparked by tougher prison searches.

The US military, which runs the camp, says those searches uncovered various banned items, including homemade weapons that have been used to attack prison guards.

The detainees' lawyers claim that during those searches the Koran was mishandled - something the US military strongly denies.

The signatories to the Lancet letter add that if detainees are ever to be transferred out of Guantanamo, they must be fit to do so.

They said doctors were "prepared to visit [the detainees] under appropriate conditions, to assist in their recovery and release, and certify when we are confident it is medically safe for them to fly".