About 150 journalists, photographers and cameramen demonstrated in Gaza City on Saturday for Israel to release the Palestinian head of Al-Jazeera's Kabul bureau.
They held a sit-in in front of UN offices to demand "the immediate release" of Samer Allawi.
Israeli authorities arrested Al-Jazeera's Kabul bureau chief on August 10 as he left the West Bank after a visit to his family.
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He was arrested trying to cross to Jordan through the Israeli-controlled Allenby Bridge, according to Al-Jazeera.
An Israeli military court in the northern West Bank has extended his detention, accusing him of "membership of Hamas" and having "contact with members in Hamas's military wing."
The demonstrators called on the United Nations to intervene against Israel's "arbitrary" detention which "violates the freedom of the press." Al-Jazeera has also urged his immediate release.
The Committee to Protect Journalists (CPJ), based in New York, has demanded Israel "clarify the legal reasons why Samer Allawi remains in detention."