Palestinian Arab and Israeli rights groups on Sunday wrote to EU foreign policy chief Catherine Ashton demanding her "urgent intervention" on behalf of 125 prisoners on long-term hunger strike.
The letter was sent as the overall number of Palestinian prisoners refusing food climbed to 290, including 70 being treated in hospital, an Israel Prisons Service spokeswoman told AFP.
Of that number, 125 have been on hunger strike for more than five weeks, beginning their mass protest on or shortly after April 24, Palestinian Arab rights groups say.
Most of the prisoners are administrative detainees who are refusing to eat in protest over their being held without trial in a procedure which can be extended indefinitely.
"We... wish to bring to your attention the ongoing mass hunger strike involving approximately 125 Palestinian detainees and prisoners, and request your urgent intervention on their behalf," said the letter, signed by 17 rights groups and the Palestinian Authority's "prisoners' affairs ministry."
"As of June 1, the majority of the hunger strikers have gone without food for 38 days.
"We have reached a critical stage and unless there is immediate intervention there will be dire consequences for the health of all those on strike," it said.
Among those refusing food are six parliamentarians from the Palestinian Legislative Council (PLC), all of whom are administrative detainees, the letter said. Palestinian Authority (PA) officials said they had only recently joined the strike.
Many had stopped taking vitamins and were only drinking water, it said, accusing Israel of withholding salt from them for the first fortnight of their strike.
Hanan Ashrawi, a senior figure with the terrorist Palestine Liberation Organization (PLO) accused Israel of "systematically" using administrative detention as a tool for the collective punishment of Palestinian Arabs.
"We call on all states... to pressure Israel to drop its cruel and illegal use of the colonial practise [sic] of administrative detention and other administrative punitive measures," she said in a statement.
The IPS denied the allegation, with spokeswoman Sivan Weizman telling AFP the detainees had been given "everything as required by law."
Several weeks ago, hundreds of Palestinian Arab terrorist prisoners declared a hunger strike in "solidarity" with a Hamas prisoner's solitary confinement. After a media brouhaha, the terrorists ended the hunger strike just hours after it began.
Some 1,550 Palestinian Arabs imprisoned in Israel ended a hunger strike in May 2012, in exchange for a package of measures which would allow visits from relatives in Gaza and the transfer of detainees out of solitary confinement.