Jerusalem (CNN) -- A group representing 1,650 Palestinian prisoners who are on a hunger strike in protest of the conditions of their detention urged Israel Thursday to start urgent talks on the treatment of prisoners.
The Palestinian Prisoner Association Club said Israel should enter a dialogue immediately with representatives of prisoners in all prisons. It also called on the United Nations and European Union to intervene on the issue.
About 150 prisoners in Israel's Ofer military prison in the West Bank joined the hunger strike Wednesday, a week after 1,500 fellow Palestinian detainees launched their action.
Another 100 are expected to join the mass protest next week, said Amani Sarahna, a media officer for the Palestinian Prisoner Association Club.
Nine of those involved have been on hunger strike for more than a month, two of them for 59 days. Fears are growing for their health, Sarahna said.
The prisoners are protesting Israel's policy of administrative detention, a controversial Israeli practice that allows authorities to detain people indefinitely. There is no requirement to charge detainees held under this practice.
The detainees also accuse Israel of mistreating prisoners by keeping them in solitary confinement for long periods, denying them visits from their families, assaulting detainees, denying medical treatment and blocking access to education.
Of the roughly 4,700 Palestinian prisoners in Israeli prisons, approximately 300 are in administrative detention.
Hassan Abed Rabo, a spokesman for the Palestinian Ministry of Detainees and ex-Detainees, told CNN that a committee of high ranking officials from within the Israeli prison service had met the representatives of prisoners inside all Israeli prisons to listen to their demands.
Rabo described the hunger strike as "the last weapon for the prisoners inside Israeli prisons to preserve their dignity and obtain their human rights."
The prisoners' demands concern their daily conditions in detention and are not political, he said.
Israeli officials are expected to decide in the coming days whether to consider the detainees' demands.
Sivan Weizman, Israeli prison service spokeswoman, confirmed that meetings had been going on but was not able to say when the decision would come.
The Palestinian Prisoner Association Club warned that it would hold Israel responsible for any harm that comes to detainees taking part in the hunger strike.
An Israeli military court has rejected an appeal by two of those on hunger strike, Bilal Diab and Thaer Halahla, challenging their detention, the club said. They have appealed to the Supreme Court.
The Supreme Court has already rejected the appeal of another prisoner, Hassan al-Safadi, the club statement said.
The mass protest follows two high-profile hunger strikes by Palestinian prisoners in recent months.
In February, Khader Adnan ended a 66-day strike after his sentence was commuted, and last month, female prisoner Hana Shalabi was deported to Gaza after refusing to eat for 44 days. Both Adnan and Shalabi were being held in administrative detention for suspected terrorist activity, according to the Israeli government.
Their hunger strikes became rallying cries for Palestinians, who staged multiple demonstrations of support in the West Bank and Gaza and launched a social media campaign to shed light on Israel's detention policies.