Ten Palestinian prisoners participating in a mass hunger strike in Israeli jails have been placed under medical supervision as their conditions worsen, officials said.
A spokeswoman for "Israel's prison service" said on Saturday that the 10 were transferred to a prison clinic for medical supervision.
Sahar Francis of Addameer, a Palestinian prisoner rights group, said the men were moved at different times last week.
She said the prisoners under medical supervision were those who had been on hunger strike the longest.
The men are among hundreds of Palestinian prisoners on hunger strike to demand better conditions and an end to detention without trial in one of the biggest prison protests in years.
At least 1,550 are taking part, although activists have said the figure is as high as 2,500 out of 4,600 Palestinians held in Israeli prisons.
Most of those participating began refusing food 19 days ago, but a smaller core have been striking for periods ranging from 40 to almost 70 days.
Another prisoner, Bilal Diab, who refused food for 68 days, was moved to a civilian hospital last week.
An independent doctor with Physicians for Human Rights-Israel said last week that Bilal was at immediate risk of death.
Addameer reported earlier this week that according to "PHR-Israel", both Bilal and another prisoner, Thaer Halahleh, were suffering "acute muscle weakness" which prevented them from standing.
Sami Hermez, an academic who specialises in non-violent resistance, told Al Jazeera that both Bilal and Thaer had not eaten for 68 days, adding that "we're getting to the critical point where prisoners may start dying and facing extreme conditions".
"[Non-violent struggle] is very effective ... hunger strikes have been used throughout the centuries to pressure governments, regimes, and occupying forces," he said.
On Thursday, WAFA, the Palestinian News and Information Agency, reported that the Israeli high court had postponed a ruling on the appeals by both prisoners for release.
The prisoners' principal demands are a halt to imprisonment without charge for periods ranging from months to years, in a system known as "administrative detention".
Other demands include being allowed to take a photo with their families once a year, instead of just once during their prison term.
Israeli officials say they use administrative detention to hold Palestinians who pose an immediate threat to the country's security.
They say they keep the evidence secret from lawyers and the accused, because it would expose their intelligence-gathering networks if it was released.
The prisoners' conditions is one of the most emotive issues for Palestinians, many of whom have had a loved one behind bars at some point.
Leading members of Hamas have warned "Israel" of consequences if any prisoners die while on hunger strike.
The latest wave of hunger strikes appears inspired by protests carried out by Palestinian prisoners Khader Adnan and Hana Shalabi earlier this year.
Adnan refused food for 66 days to demand an end to his incarceration without trial, while Shalabi refused food for 43 days.
Israeli authorities claimed both Adnan and Shalabi belonged to Islamic Jihad. Both were held in administrative detention though neither were ever charged with a crime.