This is the latest postponement to affect the long-running trial, criticized worldwide by press freedom advocates and human rights activists.
Fahmy, Australian journalist Peter Greste and Egyptian producer Baher Mohammed were detained in December 2013 while working for the Doha-based network.
The three first were sentenced to prison before Egypt's highest court ordered a retrial on charges of them allegedly being part of the Muslim Brotherhood, which authorities have declared a terrorist organization, and airing falsified footage intended to damage national security.
Egypt deported Greste in February — Fahmy and Mohammed later were released on bail.
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