Israel's Supreme Court on Monday rejected an appeal by two Palestinian prisoners who have been on hunger strike for 69 days in protest at being held without charge, their lawyer told AFP.

"The Supreme Court refused both appeals," Jamil Khatib said of the move by Bilal Diab, 27, and Thaer Halahla, 34, who had appealed to Israel's highest court on Thursday to end the administrative detention orders under which they are being held.

The Israeli courts administration confirmed their appeal had been rejected.

"They will continue their strike till the end," Khatib said.

"Israeli courts do not handle administrative detention in a positive way. It shows that the intelligence services have the final word."

Halahla was arrested on June 28, 2010 and has been held in administrative detention ever since, while Diab has been held since August 17, 2011.

Both began refusing food on February 29.

Despite the decision, Judge Elyakim Rubinstein expressed concern over the deteriorating condition of the two men, and referred the military establishment to a legal clause which could allow them to be released on parole.

The clause relates to anyone "whose illness is limiting his days, or for whom remaining in prison would seriously endanger his life due to his illness."

"This issue is worth examining in this context, on the appropriate medical basis," Rubinstein said.

He also referred to the legal difficulties in cases concerning administrative detention, an antiquated procedure that allows suspects to be held without charge for periods of up to six months, which are renewable indefinitely.

"Administrative detention causes great discontent to any judge, but it is necessary when the material regarding the petitioner is intelligence material, the exposure of which would harm its conveyor or the methods in which it was obtained."

He also proposed that the case be examined by "a jurist acceptable to the detainees, who would receive the sufficient security approval... who could examine the material on their behalf.

"This could promote the detainees' rights without harming the security."

The Physicians for Human Rights-Israel (PHR) group slammed the court ruling.

"The court's decision is a death sentence for both of them," PHR spokeswoman Amani Daif told AFP.

"Their lives are in danger and their families are still banned from seeing them," she said. "They could die any moment now."

Meanwhile, an Israeli official confirmed progress in the case of a mass hunger strike being observed by more than a third of the Palestinian prisoners being held by Israel.

As Diab and Halahla entered day 50 of their hunger strike, they were joined by another 1,200 detainees who began refusing food on April 17 in a bid to demand better conditions.

That number has now grown to "approximately 1,600 prisoners on hunger strike," Israel Prisons Service (IPS) spokeswoman Sivan Weizman told AFP on Monday.

An Israeli security official said the prisoners' demands have been examined by the prison authorities who will communicate their decision to the detainees very soon.

Among their demands are increased access to lawyers, family visits, and an end to both solitary confinement and administrative detention.

Speaking on condition of anonymity, the official said the work of the special IPS task force "has been concluded, and the team will be presenting its answers in the coming days to the prisoners who are not on hunger strike."

[A Palestinian protester holds a portrait of a jailed relative during a rally in Gaza City. AFP Photo/Mohammed Abed]