Jawad Boulos said that hunger strikers Samer al-Barq and Hassan Safadi had both been severely assaulted, after a visit to Ramle prison clinic on Wednesday.
"At 2 a.m., (Safadi) was in bed when jailers attacked him and forced him to stand and tore his clothes up and his mattress and pillow. When he tried to resist one of the jailers punched him in the face and fought with him until an officer intervened," Boulos said in a statement.
The prison administration transfered al-Barq to another prison. Using a wheelchair due to his poor health, guards at the jail asked him to stand up and walk, and when he was unable to they threw him to the ground, Boulos said.
He was sent to a clinic due to his health condition.
Al-Barq, 36, has been on hunger strike for 73 days and Hassan Safadi, 34, for 43 days.
Al-Barq, from Qalqiliya, went on hunger strike after his administrative detention was renewed and Safadi, from Nablus, restarted his hunger strike after his detention without charge was renewed in violation of the agreement ending a mass hunger strike in May.
Some 2,000 prisoners went on hunger strike in April until reaching a deal a month later when Israeli authorities pledged not to renew administrative detention orders among other agreements.