The Israeli army said Friday night that it was expanding its ground operations in the Gaza Strip amid intensifying airstrikes in its most significant maneuver yet ahead of an invasion intended to end 16 years of Hamas rule, while the strip came under a nearly complete communications blackout.

Rear Adm. Daniel Hagari, the chief Israel Defense Forces spokesman, again urged Palestinians to leave the northern Gaza Strip, including Gaza City, to head south, amid growing signs that the military was poised to launch an expansive ground operation.