At least 1,200 Palestinian prisoners in Israeli jails launched an open-ended hunger strike on Tuesday, upping the stakes in a protest movement that has put the Jewish state under pressure.

Israel has already struck deals with two Palestinian detainees this year after they staged prolonged hunger strikes and 10 other inmates have been refusing to take food in an ad-hoc campaign that has gathered unexpected momentum.

Hundreds more joined the so-called battle of empty stomachs on Tuesday to coincide with Prisoners' Day, when both the occupied West Bank and Gaza Strip stage mass rallies in support of some 4,800 prisoners who are held in Israeli prisons.

I am afraid for the life of my son. I am afraid for all their lives. All the prisoners are as dear to me as my son is, said Gaza resident Zbaida Al-Masri, adding that her son, Yusri, was serving a 20-year-term for fighting against Israel.

The Israeli prisons' authority said 2,300 prisoners had announced they would reject their daily meal on Tuesday, while 1,200 indicated they were launching a formal hunger strike.

The Israeli Prisons Authority has coped with hunger strikes in the past and is prepared to cope with it now, it added.

Palestinian officials said 1,600 prisoners were joining the indefinite hunger strike, which fits into their much broader battle to secure an independent homeland.

The hunger strikers have a long list of complaints, including the Israeli use of solitary confinement, the difficulty many having in securing family visits and the strip searches that are imposed on visitors.

Palestinians also denounce so-called administrative detention, whereby Israel can imprison suspects indefinitely, without ever informing them of the charges they face or presenting their lawyers with any evidence.

DIVIDED

Although all the main Palestinian political factions said they were backing the action, divisions swiftly appeared, with prisoners belonging to the mainstream Fatah faction accusing the Islamic group Hamas of using the campaign to divert attention from its own internal divisions.

Attempts to end a feud between President Mahmoud Abbas's Fatah movement, which holds sway in the West Bank, and Hamas, which governs Gaza, have so far failed to bear fruit.

Abbas urged the prisoners to remain united in their cause.

The sole beneficiary of the Palestinian split is Israel, the occupying power, he said in a statement. Preserve the unity of prisoners' movement, because you know what divisions and disagreements have done to our homeland and our just cause.

The start of the mass hunger strike coincides with the expected release of Khader Adnan, who refused food for 66 days before agreeing to a deal to secure his freedom.

Adnan, 33, is a member of Islamic Jihad, which has vowed to destroy Israel. Inspired by his protest, a female prisoner, Hana Shalabi, refused food for 43 days before the Israelis decided to deport her to Gaza, barring her from returning to her native West Bank for at least three years.

At the pro-prisoner rally in Gaza, boys in chains stood before the crowd as demonstrators set fire to an Israeli flag. On a nearby float, a dummy representing an Israeli soldier sat dejected-looking in an iron cage.

We demand that the Palestinian resistance carries out a second prisoner swap deal, said Ahmed Bahar, a senior Hamas politician, hinting that militants should try to seize an Israeli soldier and use him to barter for Palestinians.

Israel agreed last year to free 1,000 Palestinians in return for Gilad Shalit, a soldier held by Hamas for five years.

(Additional reporting by Ali Sawafta in Ramallah and Nidal al-Mughrabi in Gaza; editing by Crispian Balmer)