GUANTANAMO BAY, Cuba (CNN) -- Twenty-three detainees on hunger strikes at the prison camp here are being force fed to prevent their deaths, a doctor who works with the prisoners told CNN. "They are malnourished because they have hunger struck for a significant amount of time," said the doctor, who asked that his name not be used because he fears reprisals from the prisoners. Since August 8, the number of detainees refusing to eat has risen from several dozen to about 128, about a quarter of the prison population, according to the Pentagon. Though Defense Secretary Donald Rumsfeld said earlier this week that the prisoners were on hunger strikes to get media attention, the doctor said they were protesting their detention. The doctor denied that the prisoners were protesting their treatment at the prison facility.The doctor's statement also is at odds with Rumsfeld's report on Tuesday that 27 detainees were participating in hunger strikes, 24 of which were being force fed. (Read about Rumsfeld's news conference on Tuesday)Many of the facility's roughly 500 prisoners have been held for more than three years without being charged or having access to a lawyer. Most were captured in Afghanistan and are suspected of having ties to al Qaeda or the Taliban regime that formerly ruled Afghanistan. A lawyer who represents several Guantanamo detainees said one of the prisoners attempted suicide last month because of conditions at the facility."He has been in solitary confinement for almost two years. He has almost no contact with other human beings. He has one hour of exercise a week solitary in a cage," attorney Mark Sullivan said. The doctor dismissed those allegations, saying no Guantanamo detainees are placed in solitary confinement and none appears to be clinically depressed. "They see a physician on a daily basis. There's a nurse in the facility 24 hours per day, and we have not seen that," he said.U.N. investigators recently were invited to visit the facility but were not granted the same access to the detainees as the International Committee of the Red Cross. (Read about Red Cross efforts to access detainees)Red Cross reports on detainees are confidential, while the United Nations makes its findings public. Rumsfeld denied that was why the U.N. investigators weren't given access."We're not inclined to add to the number of people that would be given that extensive access," Rumsfeld said.The last hunger strike at the prison, known as Camp Delta, was in July. Sixty-eight detainees refused food, but started eating again on their own before the August 8 hunger strike, Pentagon officials said.