Two Palestinians who have been on hunger strike for 65 days appeared before Israel's Supreme Court on Thursday to appeal their detention without charge, their lawyer told AFP.

Bilal Diab and Thaer Halahla are protesting Israel's use of administrative detention, which allows military courts to order individuals held without charge for periods of up to six months, renewable indefinitely.

Jamil Khatib, who is representing both men, said his address to the court focused on what he called the "illegality" of administrative detention.

"The appeal focused on two sides, the illegality of administrative detention in general, in terms of why they are being held, and secondly why Thaer and Bilal took this step to shed light on administrative detention," Khatib said.

He said Halahla addressed the session, speaking "about his arrest and the violations that were committed against him and why he decided to go through with his hunger strike."

"He spoke about his right to a good life and his right to see his daughter, who was born while he was in administrative detention," Khatib added.

It was unclear when the court would issue a ruling on the appeal.

Judge Amnon Rubenstein "announced that the panel of judges would make a decision after reviewing the 'secret file,'" prisoner rights group Ad-Dameer said in a statement.

"But after the review (he) stated that the parties would be informed at a later time, without specifying when."

Halahla, 34, was arrested on June 28, 2010 and has been held under administrative detention orders ever since. Diab has been held since August 17, 2011 and both men began refusing food on February 29.

Officials from the Physicians for Human Rights-Israel group have warned that both men are in danger of dying, and expressed particular concern about Diab, who was transferred from a prison infirmary to a civilian hospital on Tuesday.

Khatib told AFP that Diab had fainted during the session and was treated by Arab-Israeli lawmaker Ahmed Tibi, a doctor, who was attending the hearing.

The two men have been joined on hunger strike by at least 1,550 Palestinian prisoners, the bulk of whom began refusing food on April 17.

They are calling for improved conditions, including increased access to lawyers and family visits, an end to solitary confinement and an end to administrative detention.

Palestinians across the West Bank and Gaza have staged demonstrations in solidarity with the hunger strikers, and a group of 11 Palestinian NGOs issued a statement on Thursday criticising what they called "collective and punitive measures" taken against those on hunger strike.

"These measures include solitary confinement, daily fines..., confiscation of salt for water, the denial of electricity supply and random cell and body searches," the statement said.

Israel Prison Services spokeswoman Sivan Weizman denied that prisoners were being fined but acknowledged that certain "privileges" including "television, or the right to see their family," had been rescinded.

"It's not punishment. If someone's going on hunger strike, they're saying something against the prison and they don't get a reward," she told AFP.

"If someone is on hunger strike, so it means they don't eat, so why do they need salt?"

[Israeli Arab protesters hold posters depicting Palestinian hunger strikers Thaer Halahla and Bilal Thiab via AFP / Gali Tibbon]