Sirens sounded in central and northern Israel Saturday and the Israeli military continued to pummel Lebanon and Gaza, as cease-fire talks held this week yielded little hope of ending hostilities on the ground.

Northern Gaza, already the most heavily destroyed and isolated part of the strip, has been subjected to a renewed weekslong offensive by the Israel Defense Forces, driving the area to a situation the United Nations calls “apocalyptic.”

On Saturday, Israel said its air force had…