At least 1,200 Palestinian inmates of Israeli jails began an open-ended hunger strike on Tuesday as thousands of people rallied across the occupied territories for Prisoners' Day.
As crowds gathered in towns and cities across the West Bank and the Gaza Strip, three-quarters of the 4,700 Palestinians held by Israel began refusing food, said the Israel Prisons Service.
Of that number, 2,300 men said they would refuse food throughout the day, while another 1,200 said they were beginning a hunger strike, IPS spokeswoman Sivan Weizman told AFP.
"Around 2,300 security prisoners said they were refusing their daily meals, and around 1,200 prisoners said they were starting a hunger strike," she said, adding: "We have coped with hunger strikes in the past and we are prepared to do so again now."
Palestinian officials gave a higher figure of 1,500 and said the number was set to grow in the coming weeks.
This year's Prisoners' Day took on added symbolism due to the fact it coincided with the day Israel was to release Khader Adnan, an Islamic Jihad prisoner who went on hunger strike for a record 66 days in protest at being held without charge.
Lawyer Jawad Bulus told AFP he had not been informed exactly when Adnan would be freed, but a Palestinian source said he had been discharged from Ramle prison near Tel Aviv during the afternoon and was "on his way home" to the northern West Bank.
Speaking to crowds gathered in the northern West Bank city of Nablus, Qadura Fares, head of the Palestinian Prisoners Club, said "1,500 prisoners from all the factions" had joined it already with more set to join.
"We are united and undivided when it comes to prisoners, and we will stand by them until they get their demands," he said.
In a letter smuggled out of prison, the hunger-strikers said they would continue to starve themselves until their demands were met -- or they died in the process.
"We promise our martyrs, prisoners and all of our people to go on until we grab hold of our full rights and end the policy of solitary confinement, or until we die as martyrs," said the note.
During the day, around 3,000 people gathered in Nablus, waving Palestinian flags and holding up pictures of imprisoned relatives. Hundreds more gathered in the northern towns of Tulkarem and Qalqilya.
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About 1,000 people gathered in Ramallah, and 1,500 rallied at Hebron University, waving flags and holding up pictures and slogans reading: "Stop the policy of solitary confinement."
Some 300 people also gathered by Damascus Gate outside the Old City of Jerusalem, and in Gaza City 2,000 marched to the headquarters of the Red Cross where they set up a solidarity tent with the hunger strikers.
Refusing food has become an increasingly popular form of protest for Palestinian prisoners since Khader Adnan's landmark hunger strike of nearly 10 weeks, which turned him into a national hero.
Although he stopped his strike on February 21 under terms of a deal with Israel, he was required to complete his jail term, which was to end ended on Tuesday.
Officials said it was likely he would be released during the evening at a checkpoint near Jenin.
Before Tuesday's mass protest, just 10 Palestinian inmates were on hunger strike, four of whom had been transferred to prison hospitals because of fragile health, the Palestinian Prisoners Club said.
Two of them, Bilal Diab and Thaer Halahla, have been refusing food for 50 days and are being held at the hospital wing of Ramle prison near Tel Aviv, with prisoner rights group Adameer describing their condition as "rapidly deteriorating."
Speaking to AFP in Hebron, Aziz Halahla said his son was not prepared to give up, despite his rapidly fading health.
"My son's health is deteriorating and he insists on continuing his hunger strike until they meet his demands or until he dies a martyr," he said.
Hassan Safdi, another prisoner being held in the hospital wing at Ramle after refusing food for 44 days, is also increasingly frail, with Adameer describing his condition as "very serious."
Most of them are being held without charge under administrative detention orders, which means they can be held for renewable periods of up to six months.
There are 4,699 Palestinians being held in Israeli jails, of whom 319 are in administrative detention, according to Prisoners' Club figures.