Four Israeli soldiers were killed in a Hezbollah drone attack on an army base next to the city of Binyamina, according to the military.
A statement said the strike on Sunday evening also severely injured seven soldiers.
It was the deadliest Hezbollah strike since Israel launched its ground invasion of Lebanon nearly two weeks ago.
The Lebanon-based militant group earlier claimed responsibility for the attack which was in retaliation for Israeli strikes on Beirut on Thursday that killed 22 people.
Hezbollah and Israel have traded fired almost daily in the year since the war in Gaza began, and fighting has escalated.