The Israeli military says it is calling up about 60,000 reservists ahead of a planned ground offensive to capture and occupy all of Gaza City.
A military official said the reservists would report for duty in September and that most of the troops mobilised for the offensive would be active-duty personnel.
They added that troops were already operating in the Zeitoun and Jabalia areas as part of the preparations for the plan, which Defence Minister Israel Katz approved on Tuesday and will be put to the security cabinet later this week.
Hundreds of thousands of Palestinians in Gaza City are expected to be ordered to evacuate and head to shelters in southern Gaza.