Palestinian prisoners minister Issa Qaraqaa on Tuesday warned there would be a major backlash if any of the detainees on a mass hunger inside Israeli jails were to die.
"We will not accept our prisoners returning in coffins from the occupation's prisons," Qaraqaa told a 3,000-strong crowd demonstrating in solidarity with the prisoners in the West Bank city of Nablus.
"If anything happens to any prisoner, the explosion will not stay inside prison walls but will extend to the outside," he said.
At another rally, in Gaza City, Khaled al-Batsh, a local Islamic Jihad leader, warned of possible reprisals against Israeli settlers in the occupied West Bank.
"The security of the settlers is in the hands of the prisons service," he said.
Israel dismantled its Gaza settlements in 2005.
Around a third of the 4,700 Palestinian prisoners being held in Israeli jails are currently on open-ended hunger strike, according to the Israel Prisons Service, which puts the number at 1,450.
Most have been refusing food for around two weeks, but eight of them are at an advanced stage of their hunger strike and two -- Bilal Diab and Thaer Halahla -- have gone 63 days without eating.
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A doctor with Physicians for Human Rights who examined them on Monday found they were in danger of dying and were not receiving adequate medical care where they are being held in the Ramle prison infirmary near Tel Aviv.
"I appeal from Nablus to all human rights organisations in the world to act urgently to save the lives of Bilal Diab and Thaer Halahla who are in danger of dying," Qaraqaa said.
"I hold Netanyahu's government responsible for everything that is happening to the prisoners," he said, referring to the administration of Israeli Prime Minister Benjamin Netanyahu.
Late Monday, Islamic Jihad also warned it would no longer abide by a truce agreement in Gaza if either Diab or Halahla were to die in Israeli custody.
"The death of either Bilal Diab or Thaer Halahla will nullify the truce," Jihad official Khader Habib told reporters in Gaza City.
"The enemy has to understand the message: any harm to the lives of the prisoners will lead to an escalation."
Meanwhile, 300 people gathered outside Ofer military prison near the West Bank city of Ramallah in a show of support for the prisoners.
Clashes erupted between stone-throwing youths and the Israeli army, who fired tear gas, rubber bullets and a foul-smelling liquid known as "skunk" to break up the demonstration, according to an AFP correspondent at the scene.
A photographer was badly injured after being hit in the head by a stone thrown by a protester, an AFP correspondent said.