Fifty-two detainees at the US prison camp at Guantanamo Bay in Cuba are staging a hunger strike in protest at their detention and treatment.
The US military says the men are being offered food and water
So far, the men have refused nine consecutive meals over three days, the US military said in a statement.
The detainees are being monitored by medical professionals and their vital signs are being checked daily.
More than 500 inmates are currently being held at Guantanamo. Only four have been charged.
"Indications are that this is a temporary effort by some detainees to protest their continued detention," the statement said.
On Wednesday, an Afghan man released from the camp after three years said that more than 100 prisoners had been on hunger strike for two weeks.
The former Taleban soldier said the protest was aimed at highlighting "inhuman" conditions at the camp.
However, a lawyer who represents a number of detainees held in Guantanamo Bay told BBC Pentagon correspondent Adam Brookes that protests in the prison facilities were already under way by late June.
The lawyer said that they had been prompted by detainees' anger over the quality of their drinking water.
He said the protests had then expanded in scope and detainees had begun citing their indefinite detention and inhumane conditions as reasons for the protest.
The military said the hunger strikers were being monitored by medical staff and were being admitted to hospital where clinically indicated.
Some were receiving liquids orally and intravenously and all were being offered food and water.
A military spokesman was unable to say whether any of the treatment was being administered by force.
International Committee of the Red Cross representatives are travelling to the Guantanamo Bay prison on Sunday and will be looking into the situation.