Four Israeli soldiers were killed and seven seriously wounded when a done attack by the Lebanon's Iranian-backed Hezbollah militia hit an army base about 60 kilometers (37 miles) north of Tel Aviv on Sunday, the military said.
Israeli media reported that at least 67 people were wounded in the attack on the base, which is near the Israeli town of Binyamina in central Israel.
Hezbollah claimed responsibility, saying it had fired a "squadron of attack drones" at an Israeli military training camp in the town.
Israeli broadcasters reported that many emergency services were at the scene and that no warning sirens had been activated before the projectile hit.
Israel's sophisticated air defense system usually prevents such mass casualty incidents, although Hezbollah and other groups regularly launch barrages of drones and other projectiles.
Israel, the US, Germany and several other countries consider Hezbollah to be a terror organization, while the EU deems Hezbollah's military wing a terror group.