Israel announced on Friday that it killed the commander of Hezbollah's elite unit in a strike that Lebanese officials said left 14 dead and dozens wounded in the movement's Beirut stronghold.
Ibrahim Aqil, who was wanted by the United States for involvement in the 1983 bombing of the US embassy in Beirut, headed the Iran-backed militant group's elite Radwan Force.
AFP journalists at the scene said the blast left a massive crater and gutted the lower floors of a high-rise building in the Lebanese capital's southern suburbs.
Rescue workers were still using heavy equipment to search the rubble hours after the strike, AFPTV footage showed.
Aqil's killing was the second of a senior Hezbollah commander since the start of the war in Gaza. Another Israeli strike in Beirut in July killed Fuad Shukr, a top operations chief for the movement.
It also followed two waves of explosions, on Tuesday and Wednesday, of communication devices used by Hezbollah members, which Hezbollah blamed on Israel.
Those blasts killed dozens and left Hezbollah reeling while dramatically shifting the focus of the Israel-Hamas war northwards.
Stephane Dujarric, spokesman for UN Secretary-General Antonio Guterres, said they were "of course, very concerned about the heightened escalation" and called for "maximum restraint" from all sides.
The Israeli military said it conducted a "targeted strike" to kill Aqil and which also killed around 10 other senior Radwan commanders.
A source close to Hezbollah said Aqil was "at a meeting with commanders" when he was killed.
Lebanon's health ministry said the attack killed at least 14 people and wounded 66 more, but that it expected more bodies to be found.
Earlier, a source close to Hezbollah, requesting anonymity to discuss sensitive matters, said the strike had claimed Aqil's life.
"The Israeli air strike killed Radwan Force commander Ibrahim Aqil, its armed force's second-in-command", the source close to Hezbollah said.
The movement has not officially confirmed his death, but it said after the strike that it targeted with rockets an Israeli intelligence base it blamed for unspecified "assassinations".
The United States had offered a $7 million reward for information on Aqil, describing him as a "principal member" of another organisation that claimed the 1983 embassy bombing, which killed 63 people.
- Spearhead -
Israeli troops and Hezbollah fighters have battled each other along the Israel-Lebanon border since Hamas Palestinian militants triggered the war in Gaza with their October 7 attack.
The focus of Israel's firepower for nearly a year has been on Gaza, but with Hamas much weakened, the focus of the war has moved to Israel's northern border.
Defence Minister Yoav Gallant said the countries' "enemies" would find no refuge, "not even the Dahieh in Beirut," a reference to the city's southern suburbs.
Israeli military spokesman Rear Admiral Daniel Hagari said after the strike that Israel was "not aiming for a broad escalation in the region".
Hamas, however called it a "brutal and terrorist aggression" and an "escalation".
Iran's foreign ministry accused Israel of seeking to "broaden the geography of the war".
Months of near-daily border clashes have killed hundreds in Lebanon, most of them fighters, and dozens in Israel, and forced tens of thousands on both sides to flee their homes.
The latest blow to Hezbollah came after thousands of Hezbollah operatives' pagers and walkie-talkies exploded over two days, killing 37 people and wounding thousands more.
Hezbollah chief Hassan Nasrallah vowed on Thursday that Israel would face retribution for those blasts.
Earlier Friday, Israel said Hezbollah had fired dozens of rockets from Lebanon following air strikes which destroyed dozens of the militant group's launchers.
Speaking to troops on Wednesday, Gallant said: "Hezbollah will pay an increasing price" as Israel tries to "ensure the safe return" of its citizens to border areas.
"We are at the start of a new phase in the war," he said.
Aqil's Radwan Force spearhead Hezbollah's ground operations and Israel has repeatedly demanded through international mediators that its fighters be pushed away from the border.
- 'Fear of wider war' -
Israeli Prime Minister Benjamin Netanyahu delayed by a day his scheduled departure to the United States, where he is due to address the United Nations General Assembly.
On Friday the UN's High Commissioner for Human Rights, Volker Turk, told the Security Council that the attack on Hezbollah communications devices violated international law and could constitute a war crime.
Earlier Friday, Hezbollah said it targeted at least six Israeli military bases with salvos of rockets after bombardment that people in south Lebanon described as among the fiercest so far.
Residents of Marjayoun, a Lebanese town close to the border, said the overnight bombardment was among the heaviest since the border clashes began last October.
"We were very scared, especially for my grandchildren," said Nuha Abdo, 62. "We were moving them from one room to another."
Clothing store owner Elie Rmeih, 45, counted more than 50 strikes.
"It was a terrifying scene and unlike anything we have experienced since the escalation began.
"We live in fear of a wider war."
International mediators, including the United States, have been scrambling to stop the Gaza war from turning into an all-out regional conflict.
Hamas's October 7 attacks that sparked the Gaza war resulted in the deaths of 1,205 people, mostly civilians, on the Israeli side, according to an AFP tally based on Israeli official figures that include hostages killed in captivity.
Out of 251 hostages seized by militants, 97 are still held in Gaza, including 33 the Israeli military says are dead.
Israel's retaliatory military offensive has killed at least 41,272 people in Gaza, most of them civilians, according to figures provided by the Hamas-run territory's health ministry. The United Nations has acknowledged the figures as reliable.
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