JERUSALEM  - A UN envoy called on Israel on Friday to do all it can for the health of a Palestinian prisoner who has been on hunger strike for the past 55 days in protest at his detention without charge.

Robert Serry, the UN Special Coordinator for the Middle East peace process, said he “follows with concern reports about the deteriorating conditions” of Khader Adnan, who has been refusing food since December 18 - longer than any Palestinian prisoner before him, according to Palestinian officials. Serry said he “calls on the government of Israel to do everything in its power to preserve the health of the prisoner and resolve this case while abiding by all legal obligations under international law.” Early this month, a military court ordered that Adnan be held in administrative detention for four months, although with his condition frail and worsening, he has been held mostly in a string of Israeli hospitals since early January.

On Thursday, he appealed his detention without charge before an Israeli military judge sitting in a special session in hospital, but the court is not expected to rule before Sunday, his lawyer told AFP.

Adnan, who was arrested near the northern West Bank city of Jenin, had served as a spokesman for Islamic Jihad, but Israel has not charged him formally or revealed any evidence against him.

Under Israeli military law, a court can order an individual held for up to six months at a time without charge, although the order can be appealed.

Each renewal must be approved in a new court session, but the renewals theoretically continue indefinitely.

Serry recalled that UN Secretary General Ban Ki-moon had discussed the situation of Palestinian prisoners during his visit to Israel and the occupied territories earlier this month.

Serry said that his office had been following up on the issue, particularly as regards those held without charge.

“Administrative detention... should only be employed in exceptional circumstances, for as short a period as possible and without prejudice to the rights guaranteed to prisoners,” the UN envoy said.