Anger is building up among Palestinians held in Israeli prisons, with several inmates on long-running hunger strikes in a number of prisons and clashes erupting in the Nafha jail in southern Israel.

Rights groups have warned that the health of a hunger-striking jailed Palestinian has plummeted as his fast hits 51 days.

Sami Janazrah, 43, launched his hunger strike on March 3 to protest against being held in solitary confinement and administrative detention, a practice in which Israel jails Palestinians on "secret evidence" without charges or trial.

Janazrah, who is a married father of three from the al-Fuwwar refugee camp in Hebron, is reportedly suffering from low blood pressure and arrhythmia, causing seizures and fainting spells. Meanwhile, his weight has sunk to 52 kilogrammes.

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He is one of several prisoners refusing food behind bars. Among them are also Fouad Assi and Adib Mafarjah, both of whom have been on hunger strike for 20 days.

"This could cause a lot of noise because [they] don't appear to be willing to give up the strike," said Farah Bayadsi, a lawyer at the prisoner rights group Addameer.

Of the estimated 7,000 Palestinians in Israeli lockup at the moment, at least 700 are being held as administrative detainees, according to Addameer.

"Recently there have been far more administrative detention orders," Bayadsi told Al Jazeera. "For the [Israeli] occupation, this has become the easiest way to lock up Palestinians."

A spokesperson for Israel Prison Services did not reply to Al Jazeera's requests for a comment.

Anger has spread throughout the prisoner population as tensions continue to soar over the treatment of Palestinians in Nafha, a prison in southern Israel.

Clashes erupted there between guards and prisoners on Wednesday during security checks in the facility's Section 4, where most prisoners are affiliated with the Hamas and Islamic Jihad political parties.

The guards are accused of firing tear gas and beating handcuffed prisoners.

"During the last few days there have been many attacks on Palestinian prisoners in Nafha," Bayadsi said. "What happened in Nafha is very dangerous. The situation is very bad right now."

The accusations come a week after similar charges were levelled at Israeli prison guards in Nafha following heavy clashes that left around 60 prisoners injured, according to the Palestinian Committee of Prisoners Affairs.

The prisoners branch of the Popular Front for the Liberation of Palestine, a leftist political party, released a statement on Wednesday calling for "massive popular anger against the occupation's attacks on prisoners" in Nafha.

"These days of anger come in support of the prisoners struggling to confront the attacks by the Zionist prison administration and to support the prisoners in Nafha prison facing violent attack[s]."

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On Sunday, thousands protested across the occupied West Bank, including East Jerusalem, and in the Gaza Strip on Palestinian Prisoners Day.

That same day, thousands of detainees in several prisons conducted a one-day hunger strike in solidarity with Palestinians held in Nafha.

'Always an Intifada'

The number of Palestinians behind Israeli bars has soared since October, when tensions between Israelis and Palestinians boiled over into violence.

Since October 1, Israeli forces and settlers have killed at least 208 Palestinians, including alleged attackers and protesters, according to the Palestinian health ministry.

During that period, Palestinian attackers have killed at least 29 Israelis in shooting, stabbing and car-ramming incidents, according to Israel's Ministry of Foreign Affairs.

Alaa Tartir, analyst and programme director at Al-Shabaka: The Palestinian Policy Network, explained that hunger strikes and other acts of non-compliance by prisoners have grown increasingly important against the backdrop of the current unrest.

"Although the current political leadership is letting the prisoners down and leaving them on their own, the centrality of the prisoners' plight is always significant in the popular and public conscience and this is what empowers them in their struggle," he told Al Jazeera.

Referring to the soaring tensions inside Israeli prisons, Addameer's Bayadsi said: "There is always an Intifada [uprising] inside the prisons. They have nothing to do but resist by hunger striking or similar means."

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