Expectations of an escalation had risen since a missile strike in the Israeli-occupied Golan Heights last month killed 12 youngsters and the Israeli military assassinated Shukr in Beirut in response.

In northern Israel, warning sirens sounded and multiple explosions were heard around several areas as Israel’s Iron Dome aerial defence system shot down rockets coming from southern Lebanon. Israel’s Magen David Adom ambulance service said it was on high alert all over the country.

The Israeli military issued civil defence instructions from central Israel to the north, limiting gatherings but authorising people to go to work as long as they were able to reach air raid shelters quickly. There were no casualties immediately reported in Israel, according to the ambulance service.

Israeli media said the barrage hitting northern areas had damaged some houses and a chicken coop.

A security source in Lebanon said at least 40 Israeli strikes had hit various towns in the country’s south in one of the densest bombardments since hostilities began in October.

One of the strikes on the town of Khiam killed one fighter from the Hezbollah-allied Shi’ite group Amal, two security sources told Reuters. Amal later announced his death.

A resident of the southern Lebanese town of Zibqeen, some 7 km (4 miles) from the border, told Reuters it was the first time he had awakened “to the sound of planes and the loud explosions of rockets – even before the dawn prayer. It felt like the apocalypse.”

Israel’s Army Radio, citing defence officials, said the military assessed that the Hezbollah barrage on northern Israel was “improvised” after the pre-emptive strike by Israeli jets on the Hezbollah launch sites.

President Joe Biden was following events closely, the White House said.

“At his direction, senior U.S. officials have been communicating continuously with their Israeli counterparts. We will keep supporting Israel’s right to defend itself, and we will keep working for regional stability,” said National Security Council spokesperson Sean Savett.

Hezbollah fired missiles at Israel immediately after the Oct. 7 attacks by Hamas gunmen on Israel. Hezbollah and Israel have been exchanging fire constantly ever since, while avoiding a major escalation as war rages in Gaza to the south.

That precarious balance appeared to shift after the strike in the Golan Heights, for which Hezbollah denied responsibility, and the subsequent assassination of Shukr, one of Hezbollah’s most senior military commanders.

Shukr’s death in an air strike was quickly followed by the assassination of Hamas political leader Ismail Haniyeh in Tehran, which led to vows of reprisal against Israel by Iran.