Hunger striking Guantanamo Bay detainees are being strapped to chairs for hours to force-feed them through tubes, the New York Times has reported.
Human rights groups have objected to the alleged use of force feeding
The tough treatment started after it was determined that the prisoners were trying to die, unnamed sources said.
Since December there has been a drop in the number of protesters from 84 to 4, spokesman Lt Col Jeremy M Martin said.
Human rights groups have challenged the US in the past over whether hunger strikers have been force-fed.
The US military defines a hunger strike as missing nine consecutive meals.
Responding to the New York Times article, Amnesty International renewed its call for international medical experts to be allowed to visit the strikers.
The organisation also said the US authorities should move to close the camp.
Detainees being force-fed are also restrained to stop them vomiting after feeding and placed in solitary confinement for extended periods to stop them drawing encouragement from each other, the New York Times report says.
Lt Col Martin, who is the chief military spokesman at the US detention facility, confirmed in a statement to the newspaper that "a restraint system to aid detainee feeding" was used.
But he said that force-feeding was administered "in a humane and compassionate manner" and only when necessary to keep the prisoners alive.
Citing unnamed officials, the New York Times said staff at the camp had become increasingly concerned that the hunger strike protest, which began in August, was getting out of control.
They were worried that if one of the inmates were to commit suicide it would increase international condemnation of the camp.
Despite the sudden sharp drop in the number of hunger strikers, Lt Col Martin refused to say that it was a result of the force-feeding.
"We haven't changed anything. Our processes and procedures are the same," he said. "But the numbers have fluctuated."
Held without charge
The hunger strikes began last summer as a protest against conditions at the prison, with 76 prisoners taking part. The number rose to 131 in September, then fell away, before rising again to 84 in December.
The camp was set up in 2002 to hold foreign terror suspects, many of them captured in Afghanistan. It currently houses around 500.
According to a report by two lawyers more than half of the detainees, who are being held without charge, have never committed any "hostile acts" against the US.
Mark Denbeaux and Joshua Denbeaux estimated that 55% "are not determined to have committed any hostile acts against the United States or its coalition allies", after analysing government documents regarding the prisoners.
They said that according to the documents only 8% were classed as al-Qaeda fighters and 60 prisoners "are detained merely because they are 'associated with' a group or groups the [US] government asserts are terrorist organizations".
The report also suggests that some of the detainees were caught by people seeking US bounties and their identities were never properly verified.