More: Prime Minister Benjamin Netanyahu of Israel said in a statement that he had ordered the Israeli military to attack the southern outskirts of Beirut, known as Dahiya, as part of the widening Israeli campaign against Hezbollah, the powerful Iran-backed militia. Israel has mostly refrained from attacking the city since the U.S.-Iran cease-fire took effect in early April, but it has continued to bombard southern and eastern Lebanon. Hezbollah has fired on both Israeli soldiers in Lebanon and targets in northern Israel.

The announcement by Mr. Netanyahu prompted thousands of residents to flee their homes, clogging the roads out of the area late Monday morning. For many residents, the sudden exodus has become a miserable routine over nearly three years of conflicts between Hezbollah and Israel.