More than half of the men held at the Guantanamo detention camp have joined an escalating hunger strike to protest their open-ended detention, a camp spokesperson has said.
The US military counted 84 of the 166 prisoners as hunger strikers by Monday, and was force-feeding 16 of them liquid meals through tubes inserted in their noses and down into their stomachs.
Six were hospitalised for observation, said Lieutenant Colonel Samuel House, a spokesperson for the detention operation at the Guantanamo Bay US Naval Base in southeastern Cuba.
The US military is sending additional medical personnel to the prison camp to handle the hunger strikers, House said on Monday.
Reinforcements numbering fewer than 40 will arrive by the end of April.
House said the new arrivals would include a doctor, nurses, corpsmen and medics, who will supplement the 100 medical personnel already on duty. Navy hospital corpsmen and Army medics are trained to provide emergency care and basic medical services.
"There was no specific trigger, other than the growing number of detainees that have chosen to hunger strike," House said.
Hunger strikes have occurred at Guantanamo since shortly after the United States began detaining suspected al-Qaeda and Taliban captives there in January 2002.
The current hunger strike began in early February, after guards seized photos and other belongings during a cell search.
Prisoners said the guards had also mistreated their Qurans during the search, which the US military denies.
The military has declined to say what prompted the cell searches but similar searches have been conducted in the past.
Though the cell search was the immediate trigger, military officials and lawyers for the prisoners have said the protest generally reflects frustration with the failure to resolve the prisoners' fate. Most have been held for more than a decade without charge or trial and Congress has blocked Obama administration efforts to close the camp.
"It's escalated because the men are desperate and they've hit a breaking point," said Carlos Warner, a federal public defender from Ohio who is part of a team representing 11 Guantanamo prisoners.
"Really what is behind all this is the president abandoned his promise to close Guantanamo. The men know that, they're desperate."
Forty-three prisoners had joined the hunger strike by April 13, when guards in riot gear swept through a communal prison and forced the detainees into one-man cells where they could be better monitored. Camp officials said the detainees had covered the security cameras and windows, blocking guards' view.
The number refusing meals has grown steadily since then, and two prisoners tried to kill themselves by making nooses with their clothing, House said.
Lawyers for the prisoners have said the hunger strike is more widespread than the military acknowledges, with between 100 and 130 detainees taking part.
More than half of Guantanamo's prisoners have been cleared for release but Congress has put stringent restrictions on transfers.
About two-thirds of those cleared for release are Yemenis and the Obama administration has halted repatriations to their homeland because of instability there.