At least 1,200 Palestinian inmates of Israeli jails began an open-ended hunger strike on Tuesday as rallies across the occupied territories marked Prisoners' Day.
As thousands gathered in towns and cities in both the West Bank and the Gaza Strip, three-quarters of the 4,700 Palestinians held by Israel began refusing food, the Israel Prisons Service (IPS) said.
Of that number, 2,300 male and eight female prisoners 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.
"In the framework of Prisoners' Day, around 2,300 security prisoners said they were refusing their daily meals, and around 1,200 prisoners said they were starting a hunger strike," Weizman said.
"At IPS, we have coped with hunger strikes in the past and we are prepared to do so again now," she added.
Speaking to crowds gathered in the northern West Bank city of Nablus, Qadura Fares, head of the Palestinian Prisoners Club, gave a higher figure for the hunger strike, saying "1,500 prisoners from all the factions" had joined it already and more were expected to later in the month.
"We are united and undivided when it comes to prisoners, and we will stand by them until they get their demands," he said.
Earlier this week, prisoners minister Issa Qaraqaa told AFP that 1,600 inmates were expected to join the strike, and on Tuesday he said the initial number was likely to grow.
"Our estimations were that 1,600 prisoners would begin a hunger strike but there was a difference of opinion between the prisoners which prevented all of them from joining the hunger strike," he told AFP.
"But this number is likely to increase in the coming days."
Throughout the morning, thousands of people held marches and rallies across the West Bank, with around 3,000 people gathering in Shuhada Square in central Nablus, waving Palestinian flags and holding up pictures of imprisoned relatives.
Another 1,000 or so people gathered in central Ramallah, with a sit-in planned for later in the afternoon outside the nearby Ofer prison.
In the southern West Bank city of Hebron, 1,500 people gathered holding up flags, pictures and slogans reading: "Stop the policy of solitary confinement."
Hundreds more gathered in the northern towns of Tulkarem and Qalqilya, AFP correspondents said.
In Gaza City, around 2,000 people marched to the headquarters of the Red Cross where they set up a solidarity tent with the hunger strikers.
This year's Prisoners' Day took on added symbolism as it was also the day when 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.
Adnan, whose nearly 10-week fast turned him into a national hero, was to be freed later on Tuesday, although it was not clear exactly when or where, his lawyer said.
Before Tuesday's action, 10 Palestinian inmates of Israeli prisons were already 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, 27, and Thaer Halahla, 34, had been refusing food for 50 days.
They were both being held in the hospital wing of Ramle prison near Tel Aviv, with prisoner rights group Adameer describing their condition as "rapidly deteriorating."
Another prisoner, Hassan Safdi, on hunger strike for 44 days, was being held in the same facility, with his condition described as ""very serious."
All 10 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.