Palestinian president Mahmud Abbas warned on Sunday of a "national disaster" if any of the 1,550 Palestinian prisoners on hunger strike in Israeli jails were to die.
Abbas spoke as two of the hunger strikers, Bilal Diab and Thaer Halahla, entered their 75th day without eating, and after international rights groups and governments said they were concerned that prisoners could die if they continued to refuse food.
"The situation of the prisoners is extremely dangerous," Abbas told a meeting of the Palestine Liberation Organisation's executive committee.
"Some of them face real harm, and that would be a national disaster that no one can tolerate. I hope and pray to God that no one gets hurt because it would be a major disaster."
The committee called on all Palestinians to observe a one-day fast on Monday in solidarity with the prisoners.
Diab and Halahla are specifically protesting their jailing by Israeli authorities without charge under a procedure known as administrative detention.
The broader hunger strike by around 1,550 Palestinian prisoners is intended to pressure Israeli prison authorities to end the use of solitary confinement and ease a wide range of restrictions, including on family visits and prisoner education.
Hamas deputy chief Mussa Abu Marzuk said that following Egyptian intervention on the issue it had been close to resolution but talks stalled "two days ago."
"There was an Israeli commitment to meet the demands of the hunger striking prisoners, in particular on the issue of moving them out of isolation and visits by the families of the prisoners," he told AFP.
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"But there were disagreements among the Israelis after that and nothing was achieved."
However, a source close to the dispute said a deal hammered out in the Egyptian capital would be submitted to prisoners on Monday.
Israeli and Palestinian demonstrators gathered on Sunday outside the West Bank settlement of Maaleh Adumim in a show of solidarity with he prisoners. Israeli police said two of the Palestinians were arrested for blocking a public road.
The hunger strike has attracted widespread support throughout the Palestinian territories, and Abbas said he had raised the issue in discussions with Israeli negotiator Yitzhak Molcho and US Secretary of State Hillary Clinton.
"These prisoners have a right to justice, and we are talking about the conditions of detention and the prison conditions that Israel is trying to ignore," Abbas said. "The issue of the prisoners is the most important issue we're working on these days."
Palestinian sources say negotiations are under way with Israeli representatives on a package of measures to ease conditions for the 4,700 Palestinians held in Israeli jails.
The measures would include restarting family visits for prisoners with relatives in Gaza, allowing detainees to resume studies and moving some inmates out of solitary confinement.
A Palestinian official who spoke to AFP on condition of anonymity said a key meeting of Israeli officials was taking place Sunday with representatives of the Israel Prisons Service (IPS), the domestic intelligence service Shin Bet and Israel's government.
But an IPS spokeswoman said she had no knowledge of such a meeting.