The strike entered its 21st day Sunday. Israel says 890 prisoners are participating.
Qadoura Fares, head of an advocacy group for Palestinian prisoners, says the hunger strikers began taking supplements on day 15. He says guards stepped up punishment, seizing all personal items and leaving prisoners “with nothing except their beds.”
Fares says strike organizer and Palestinian uprising leader Marwan Barghouti remains in solidarity confinement. He says the information comes from lawyers who recently visited the strikers.
The spokesman for the Israel Prison Service could not be reached for comment.
The prisoners seek improved conditions, including more family visits.
Israel holds about 6,500 Palestinians on charges related to the Israeli-Palestinian conflict.