Israel killed militant group Hezbollah's top military official in an airstrike on a southern suburb of Beirut on Sunday, the Israeli military said, despite a US-brokered truce a year ago.

The strike, the first on the outskirts of the Lebanese capital in months, targeted Iran-backed Hezbollah's acting chief of staff, Ali Tabtabai, the military said in a statement.

Hezbollah confirmed the death of Tabtabai in a statement, mourning him as "the great jihadist commander" who had "worked to confront Israeli enemy until the last moment of his blessed life," showing his seniority, but without giving details about his exact role.

Israel's strike crossed a "red line", Hezbollah official Mahmoud Qmati said as he stood near the bombed-out building in the Haret Hreik suburb, a Hezbollah stronghold.

Hezbollah's leadership would decide on whether and how the group would respond, he added.

Five dead in strike

Lebanon's health ministry said the strike killed five people and wounded 28 more. It hit a multi-storey building, sending debris crashing into cars on the main road below.

People rushed out of their apartment buildings, fearing further bombardment, a Reuters reporter said.

The United States imposed sanctions on Tabtabai in 2016, identifying him as a key Hezbollah leader and offering a reward of up to $5 million for information on him.

The Israeli military statement said Tabtabai "commanded most of Hezbollah's units and worked hard to restore them to readiness for war with Israel".

In a short televised statement, Israeli Prime Minister Benjamin Netanyahu said Israel would not allow Hezbollah to rebuild its forces and that he expected the Lebanese government "to fulfill its obligation to disarm Hezbollah."

Lebanese President Joseph Aoun urged the international community to intervene to halt Israeli attacks.

The strike came a week before Pope Leo is set to land in Lebanon on his first foreign trip, with many Lebanese hoping the visit could signal the country was heading towards better days.

The November 2024 ceasefire was meant to end a year of fighting between Hezbollah and the Israeli military, triggered by Hezbollah's rocket fire on Israeli posts a day after the October 7, 2023 attack by its Palestinian ally Hamas.

But Israel has kept up near-daily strikes on Lebanon since the truce, targeting what it says are Hezbollah arms depots, fighters and efforts by the group to rebuild. It has ratcheted up those strikes in recent weeks.

Asked if Israel had notified the U.S. before carrying out the strike, Israeli government spokesperson Shosh Bedrosian said Israel makes decisions independently.

Israel already killed much of Hezbollah's leadership

Israel eliminated much of the group's leadership during the year-long war, including its then-leader Hassan Nasrallah.

Israel and Lebanon have traded blame over ceasefire violations since 2024.

Lebanon says Israel's continuing strikes and occupation of five southern posts in Lebanese territories are major breaches. Aoun says he is open to negotiations but has not received a positive response from Israeli officials.

Israel accuses Hezbollah of trying to regroup in the south, and is pressuring Lebanon to be more aggressive in confiscating all unauthorised arms across the country, including Hezbollah's.

Hezbollah has not fired on Israel since the ceasefire started and says it is abiding by it.