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Former Afghan Guatanamo prisoners Moheb Ullah Borekzai, left, and Habir Russol, get out of the car that took them to their release ceremony in Kabul, Afghanistan. (AP Photo)

At least 52 prisoners are taking part in a hunger strike at the U.S. prison camp at Guantanamo Bay, Cuba, the U.S. military has confirmed.

"Indications are that this is a temporary effort by some detainees to protest their continued detention," the U.S. military said in a statement Thursday.

It said detainees refusing meals have been given water, a high-energy sports drink, a liquid nutritional supplement and intravenous hydration. As well, some may be admitted to the hospital.

However, a military spokesman was unable to say if any of the treatment was being administered by force.

Representatives from the Red Cross will be going to Guantanamo Bay on Sunday to check on the detainees.

The Centre for Constitutional Rights, a U.S. human rights group based in New York, says the hunger strike has been going on since late last month.

There are conflicting reports about how many prisoners may be involved.

On Wednesday, two Afghans who'd just been released from Guantanamo Bay put the number of hunger strikers at about 180. Habir Russol and Moheb Ullah Borekzai told the Associated Press in Kabul they were not part of the protest.

"Some of these people say they were mistreated during interrogation. Some say they are innocent," Borekzai said.

"They are protesting that they have been in jail nearly four years and they want to be released," he said.

At least 500 people are being held at Guantanamo Bay, despite repeated calls by human rights organizations for the U.S. to either charge or release them.

Many of them were detained in Afghanistan when the U.S. and its allies invaded the country in late 2001, looking for al-Qaeda leader Osama bin Laden and determined to overthrow the extremist Taliban regime that had sheltered him.