The protest gathering also marked Islamic Jihad official Khader Adnan's 44 days of refusal to eat at an Israeli prison.
Adnan, who was arrested by Israeli troops on December 17, started a hunger strike the following day to protest being imprisoned without trial.
Rights group Physicians for Human Rights said in a statement on Monday that Adnan's life is in danger.
"His health is deteriorating and his life will be in danger if he continues the hunger strike. He does not eat and only drinks water," the group said in a statement after its doctors examined him, adding that Adna's trial at a military court was postponed until February 1 over his deteriorating health.
Israeli prison authorities, however, claims that his condition is satisfactory.
"If necessary he will be taken to a hospital for further treatment," she said. "All the effects of hunger-striking have been explained to him... We shall consider forced feeding if it becomes necessary."