An Israeli military court on Sunday rejected the appeal of a Palestinian woman who has been on hunger strike for 39 days, her lawyer told AFP.
Hanaa Shalabi was appealing a four-month administrative detention order allowing her to be held without charge.
"The Israeli military court rejected the appeal and now we will go to the High Court," Jawad Bulus said. "Hanaa will continue her hunger strike."
Shalabi was detained on February 16, and a military court initially ordered her to be held for six months. That was later reduced to four months, the decision she unsuccessfully appealed.
Shalabi has been on hunger strike since her arrest, to protest both her detention without charge and violence she says was inflicted during her arrest.
On Friday, rights group Amnesty International urged Israel to prosecute or free Shalabi, saying she was "at risk of death."
She was hospitalised on March 19, after 33 days without food, with doctors saying she had lost 14 kilos (31 pounds) and her pulse was "feeble."
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Shalabi was among more than 1,000 Palestinian prisoners released in October in exchange for Israeli soldier Gilad Shalit, held by Gaza Strip-based militants for more than five years.
She had been held by Israel for more than two years without charge before she was released under the prisoner exchange.
The Israeli army has said she is "a global jihad-affiliated operative" who was re-arrested on suspicion that she "posed a threat to the area."
But no charges have been filed against her and no specific allegations have been made public.
Shalabi is one of around 300 Palestinian prisoners being held in Israeli jails under administrative detention orders, which allow a court to order an individual to be detained for periods of up to six months at a time.
Her hunger strike follows one undertaken by another Palestinian prisoner, Khader Adnan, who was also protesting his administrative detention.
Adnan refused food for 66 days, only agreeing to end his hunger strike after a deal was struck ensuring he would be released at the end of his four-month term.
In the wake of his hunger strike, dozens more Palestinian prisoners in Israeli jails have undertaken similar protests, according to Palestinian and Israeli officials.
Shalabi's case has attracted support across the Palestinian territories, as did Adnan's, with Palestinians holding demonstrations in solidarity with her and other prisoners in both the West Bank and Gaza Strip.