The Pentagon said Monday 39 men were consistently refusing food and 11 of those were being force-fed, The Washington Post reported.
Attorneys for the detainees said they were told nearly all inmates of Camp 6 -- where detainees can use common areas -- were on hunger strike. Until recently, 130 men were housed in Camp 6. The lawyers said some protesters were moved to Camp 5, which has been used to hold "non-compliant" detainees in greater isolation.
Military officials wouldn't release the population for the specific camps, the Post said. The facility has 166 detainees overall.
Attorneys for the detainees said the immediate cause for the protest, which started in February, was a decision to search detainees' Korans. Military officials said Korans were searched for contraband but were handled by interpreters, most of whom are Muslim, not guards.
David Remes, a lawyer for some detainees, said most of the strikers would resume food intake if the military agreed not to search Korans. However, several men indicated they wanted to expand the strike to protest their detention and what they consider the Obama administration's desertion of its plans to close the facility, Remes said.
The International Committee of the Red Cross said 13 delegates are visiting the camps.
"It is the opinion of the ICRC that past and current tensions at Guantanamo, including hunger strikes, are the direct result of the uncertainty faced by detainees," Simon Schorno, a spokesman for the organization, said in a statement issued Monday.
Human Rights Watch on Monday called on Defense Secretary Chuck Hagel to allow it "full access to Guantanamo Bay detention camps so that we can independently review and report on the conditions of confinement."