RAMALLAH, West Bank — Hundreds of Palestinian prisoners held by Israel launched a hunger strike on Tuesday, officials said, protesting their conditions and demanding an end to open-ended detentions without trial as the Palestinians marked their annual day of solidarity with the inmates.

Some 3,500 prisoners refused meals on "Prisoners' Day," and 1,200 of them said they would continue with an open-ended hunger strike, according to Israeli prison service spokeswoman Sivan Weizman.

The mass hunger strike is one of the largest on record, said Sahar Francis of Addameer, a prisoner rights group.

Although it remains unclear how many will continue with the protest, they join 10 other Palestinian prisoners already on hunger strike, including two who have been hospitalized after refusing food for more than 40 days, she said.

The days' activities, which included protests throughout the West Bank and Gaza Strip, coincided with the scheduled release of the longest hunger striker in Palestinian history.

Khadnan Adnan, who didn't eat for 66 days, was set to be freed later Tuesday as part of a deal reached with Israel.

Adnan, a spokesman of the violent Islamic Jihad group, called his strike to protest Israel's policy of "administrative detention," in which Palestinians can be sentenced to months or years behind bars by military courts without being charged. In February, Israel agreed to release him at the end of his detention in exchange for ending the hunger strike.

"He began the first step for the rest of the prisoners," said his wife Randa, referring to Tuesday's hunger strike.

In his West Bank hometown of Arrabeh, well-wishers decked posters of Adnan on the streets, and the family prepared to slaughter a sheep in his honor.

The fate of the prisoners held by Israel is one of the most emotional issues in Palestinian society. Their crimes range from throwing stones to deadly militant attacks. They are generally seen as heroes — even when their crimes have involved killing civilians.

In demonstrations throughout the Palestinian areas, hundreds of people held framed pictures of their loved ones in prison and waved the brightly colored flags of different Palestinian political factions.

At a military prison near Jerusalem, Palestinian youths hurled rocks at Israeli forces who fired back rounds of tear gas and pellets. No injuries were reported.

There are some 4,000 Palestinians currently in Israeli jails, said Francis, including some 300 in administrative detention. The striking prisoners are demanding an end to such detentions, solitary confinement and to allow Gaza families to visit prisoners held in Israel.

The largest Palestinian prisoner strike was in 2004, when some 10,000 prisoners refused food, many of them for 17 days, Francis said.