BETHLEHEM (Ma'an) -- UN Secretary-General Ban Ki-moon on Wednesday urged Israel to either charge or release Palestinian detainees "without delay."

Ban expressed concern for Palestinian prisoners on hunger strike in protest over their detention without charge and stressed "the importance of averting any further deterioration in their condition," in a statement issued through his spokesman Martin Nesirky.

"(Ban) reiterates that those detained must be charged and face trial with judicial guarantees, or released without delay," the statement added.

Thaer Halahla, 33, and Bilal Diab, 27, have been on hunger strike in Israel jail for 72 days. Neither has been charged or tried for any offense.

On Monday, Israel's Supreme Court rejected appeals against their administrative detention.

Physicians for Human Rights - Israel said Diab was transferred from hospital to a prison clinic on Tuesday.

"The (Israeli Prison Service) clinic is not adequate both ethically and professionally to treat hunger strikers. For a life saving resolution to have a chance, hunger strikers must be hospitalized," PHR-I said in a statement.

The International Committee of the Red Cross warned Tuesday that Diab, Halahla and four others on hunger strike were in "imminent danger of dying" and called on Israel to transfer them to hospital and allow visits from their families.

Thousands of Palestinian detainees are refusing food to protest Israeli policies, including detention without charge, denial of family visits and solitary confinement.

On Wednesday, protesters blocked the entrance to the UN office in Ramallah slamming the world body for its failure to intervene to save the hunger strikers.

A group of youth activists called Palestinians for Dignity sent a letter to Ban Ki-moon on Monday, urging him to take a "firm and vocal position in opposition to Israel’s abuse and violation of Palestinian prisoners' rights."

The letter added: "We note with disappointment your silence ever since this protest movement began in December 2011 with Khader Adnan’s arbitrary arrest and subsequent hunger strike."

"This stands in stark contrast to your vocal and persistent remarks in support of formerly incarcerated Israeli soldier Gilad Shalit."