Israel says it has killed top Hezbollah commander Ibrahim Aqil and around 10 other senior figures from the militant group an airstrike in southern Beirut on Friday.
Lebanon's health ministry said Friday's strike killed 12 people and wounded 66 others, nine of whom were in critical condition.
The Israeli military said it killed Aqil, who it identified as the acting commander of the Radwan special forces unit, and around 10 senior commanders as they held a meeting.
The strike inflicted another blow on Hezbollah after an unprecedented attack on the group this week in which pagers and walkie-talkies used by its members exploded, killing 37 people and wounding thousands. That attack was widely believed to have been carried out by Israel, which has neither confirmed or denied its involvement.
Hezbollah is yet to comment on the reports Aqil and other seniors figures were killed.
The US justice department had designated Aqil as a global terrorist for his alleged role in the 1983 US embassy bombings in Beirut which killed 63 people, as well as the US Marine barracks attacks that year that killed 241 US personnel.
The Israeli military said Aqil had been head of Hezbollah operations since 2004 and was responsible for a plan to launch a raid on northern Israel, similar to the Hamas-led attack on southern Israel on October 7 that triggered the war in Gaza.
Israel said earlier it had carried out a “targeted strike” on Beirut, deepening concerns about a full-scale war with Hezbollah.
A thick cloud of smoke could be seen rising over the capital, according to a Reuters live feed, after residents said they heard a loud blast.
"The IDF (Israel Defence Forces) conducted a targeted strike in Beirut. At this moment, there are no changes in the Home Front Command defensive guidelines," the Israeli military said.
The strike came after Hezbollah pounded Israel with 140 rockets, which the Israeli military said came in three waves targeting sites along the ravaged border with Lebanon.
Israel also carried out its most intense air strikes on southern Lebanon in nearly a year of war.
Israel's military said jets struck hundreds of multiple-rocket-launcher barrels in southern Lebanon on Thursday that were set to be fired immediately toward Israel.
The bombardment included more than 52 strikes across southern Lebanon after 9pm, Lebanon's state news agency NNA said.
Three Lebanese security sources said these were the heaviest aerial strikes since the conflict began in October.
There were no immediate reports of casualties.
Israel's military has vowed to continue to attack Hezbollah and said its strikes throughout Thursday hit about 100 rocket launchers plus other targets in southern Lebanon.
Hezbollah said that its attacks had targeted several sites along the border with Katyusha rockets, including multiple air defence bases as well as the headquarters of an Israeli armoured brigade they said they struck for the first time.
The Israeli military said that 120 missiles were launched at areas of the Golan Heights, Safed and the Upper Galilee, some of which were intercepted. Fire crews were working to extinguish blazes caused by pieces of debris that fell to the ground in several areas.
Another 20 missiles were shot at the areas of Meron and Netua and most fell in open areas, the military said, adding that no injuries were reported.
Hezbollah said that the rockets were in retaliation for Israeli strikes on villages and homes in southern Lebanon.
Meanwhile, the White House has called for an urgent diplomatic solution while the UK has called for an immediate ceasefire between Israel and the Lebanese armed group.
The US is "afraid and concerned about potential escalation," White House spokesperson Karine Jean-Pierre told a briefing.
The intense barrage on Thursday followed the two deadly attacks targeting Lebanese militants with exploding pagers and walkie-talkies in which the dead included two children.
The attacks have been blamed on Israel’s spy agency by Lebanon and Hezbollah.
In a TV address on Thursday, Hezbollah leader Hassan Nasrallah said the device explosions on Tuesday and Wednesday "crossed all red lines".
"The enemy went beyond all controls, laws and morals," he said, adding the attacks "could be considered war crimes or a declaration of war."
Israel has not directly commented on the pager and radio detonations, which security sources say were probably carried out by its Mossad spy agency, which has a long history of carrying out sophisticated attacks on foreign soil.
The Lebanese mission to the UN said in a letter to the Security Council on Thursday that Israel was responsible for detonating the devices via electronic messages and explosives implanted in them before they arrived in Lebanon, in line with theories that have circulated since the explosions.
The 15-member Security Council is due to meet on Friday over the blasts. Lebanese Prime Minister Najib Mikati called on the Security Council to take a firm stand to stop Israel's "aggression" and "technological war".
As Nasrallah's broadcast aired, deafening sonic booms from Israeli warplanes shook Beirut.
Israeli Defence Minister Yoav Gallant said late on Thursday that Israel will keep up military action against Hezbollah.
"In the new phase of the war there are significant opportunities but also significant risks. Hezbollah feels that it is being persecuted and the sequence of military actions will continue," Gallant said in a statement.
"Our goal is to ensure the safe return of Israel's northern communities to their homes. As time goes by, Hezbollah will pay an increasing price," Gallant said.
Prime Minister Benjamin Netanyahu convened his close circle of ministers for consultations, Israel's Channel 13 News reported.
Two Israeli soldiers were killed in combat on Thursday in Israel's north, the Israeli military said.
