The Palestinian Prisoners' Society (PPS) accused Israel on Monday of killing a senior leader of Hamas who was being held in an Israeli prison.
In a statement, PPS said Omar Daraghmeh, 58, was arrested on Oct. 9 and placed under administrative detention.
It said the Israeli narrative about the circumstances of Daraghmeh's death "remains subject to doubt," particularly since he had appeared at a court hearing earlier in the day and seemed to be in good health.
An Israeli statement claimed his death was due to a heart attack.
The Palestinian Hamas group mourned the death of Daraghmeh as one of its senior leaders in the occupied West Bank and held Israel responsible, describing it as an "assassination."
A demonstration took place in his hometown of Tubas to protest his death.
Israeli forces have arrested more than 800 Palestinians across the West Bank since fighting broke out between Palestinian groups and Israel on Oct. 7.
