JERUSALEM — A Palestinian woman who has refused food for the past month to protest her imprisonment by Israel without formal charges is in grave danger of dying, a medical rights group said Tuesday.

Hana Shalabi lost 14 kilograms (31 pounds), her muscles are wasting and she is in excruciating pain, said Ran Cohen of Physicians for Human Rights-Israel, which has provided her a doctor. She has taken only water since her arrest on Feb. 16.

“We are worried. Her physician has demanded she be transferred to hospital,” said Cohen. Israel Prison Service spokeswoman Sivan Weizman said that for the time being, Shalabi is being monitored at a prison clinic.

Shalabi, 30, a supporter of the militant Islamic Jihad group, is being held without formal charges, an Israeli system called “administrative detention.” She is scheduled to be released in another three months.

Israeli military officials say they use administrative detention to hold people who pose an immediate risk to the country’s security, or when displaying incriminating evidence would reveal Israeli intelligence-gathering networks.

More than 300 of some 6,000 Palestinians currently held by Israel on security-related charges are in administrative detention. Rights activists say international law allows this practice only in exceptional cases and that Israel blatantly violates these restrictions.

Prison authorities say 20 Palestinian detainees have launched hunger strikes in support of Shalabi in the past two weeks. Earlier this year, administrative detainee Khader Adnan staged a hunger strike for 66 days. He ended the protest after reaching a deal with the Israeli authorities to free him in April.

Also Tuesday, a U.N. agency urged Israel to crack down on settler takeovers of springs on Palestinian land in the West Bank and restore the water sources to their original owners.

Israeli settlers have used intimidation and fencing to block Palestinians from using 30 springs in the West Bank, according to a report by the U.N. Office for the Coordination of Humanitarian Affairs. In another 26 cases, settlers have made attempts to take the springs over, including renaming them in Hebrew, running frequent tours and building infrastructure like benches, pools and shading, the report found.

Nearly all these springs are on private Palestinian land, but Israeli law enforcement has done little to restrain the settlers, OCHA reported. The West Bank has several hundred springs, the report said.

The Israeli military said the report was “distorted, biased and full of inaccuracies.” It pointed to two springs where the military was enforcing the law.

In other developments, Palestinian President Mahmoud Abbas and President Barack Obama spoke by phone for the first time in six months.

In Monday’s conversation, Abbas assured Obama that a letter he plans to send to Israeli Prime Minister Benjamin Netanyahu in coming days will not contain an ultimatum, according to an Abbas aide who spoke on condition of anonymity because he was not authorized to discuss the content of the conversation.

Abbas has said the letter will sum up peace efforts, remind Israel of its peace obligations and lay out the requirements for renewing negotiations, including an Israeli settlement freeze. Netanyahu has refused to halt construction for Jews on occupied lands the Palestinians want for their state.

Negotiations broke off in late 2008, and Abbas has said there is no point negotiating with the hard-line Netanyahu unless he gets ironclad assurances about a settlement freeze and the parameters for talks.

Palestinians initially said the letter would include an ultimatum: a deadline for an Israeli response, and that once that deadline had passed, they would feel free to resume their quest for world recognition of a state of Palestine.

However, under growing U.S. pressure, they decided not to set a deadline in the letter, officials have said. Instead, the Palestinian leadership is to convene after a certain period to consider its next steps.