Eighty-four of the 166 prisoners held at the US-run Guantanamo Bay facility are now on hunger strike, US military officials have said.
The prisoners are protesting against their indefinite detention. Most are being held without charge.
Sixteen of the 84 prisoners are being force-fed and five are being treated in hospital. None has a life-threatening condition, according to the military.
The hunger strike started in February and has grown rapidly in recent weeks.
The number of strikers last Wednesday was 52 and by Friday had reached 63.
‘Mishandling of the Koran’
Hunger strikes are frequent at Guantanamo, but the current protest – which began on 6 February – is one of the longest and most widespread.
Guantanamo officials deny claims that the strike began after copies of the Koran were mishandled during searches of prisoners’ cells.
Violence erupted at the prison on 13 April as the authorities moved inmates out of communal cellblocks where they had covered surveillance cameras and windows.
“We were trying to be patient and work with them and give them the opportunity to comply. We hit the point where… I felt we were accepting too much risk and it was time to take action,” said Colonel John Bogdan.
Some prisoners used “improvised weapons” and were met with “less-than-lethal rounds”, a military spokesman said, but no serious injuries were reported.
Nearly 100 of the detainees have reportedly been cleared for release but remain at the facility because of restrictions imposed by Congress and also concerns of possible mistreatment if they are sent back to their home countries.