The most prominent Palestinian prisoner, Marwan Barghouti, was beaten unconscious by Israeli prison guards on 14 September, his family has said.
The 66-year-old - serving life for planning deadly attacks against Israelis - was allegedly attacked by eight guards during a transfer between Ganot and Megiddo prisons.
The Israel Prison Service told the BBC: "These are false claims (fake). The Israel Prison Service operates in accordance with the law, while ensuring the safety and health of all inmates".
Barghouti's son, Arab, told the BBC the family had received testimony from five separate detainees who were released this week who heard Barghouti's account of the attack. He said the family was "horrified".
Barghouti was allegedly handcuffed by the guards, put on the floor, kicked and beaten.
