The leader of Hezbollah acknowledged on Thursday that his group had suffered a "major and unprecedented" blow after thousands of operatives' communication devices exploded across Lebanon in deadly attacks it blamed on Israel.

In his first speech since the attacks, which killed 37 people and wounded nearly 3,000 more across two days, Hassan Nasrallah also struck a defiant tone, vowing that Israel would face a "just punishment."

Even as he delivered his televised address, Israeli warplanes broke the sound barrier over Beirut.

Describing the attacks as a "massacre" and as a possible "act of war," Nasrallah said Israel would face "tough retribution and a just punishment, where it expects it and where it does not."

Israel has not commented on the attacks in which Hezbollah operatives' pagers and walkie-talkies exploded in supermarkets, on streets and at funerals, plunging the country into panic.

But its defence minister, Yoav Gallant, said on Wednesday, in reference to Israel's border with Lebanon: "The centre of gravity is moving northward."

"We are at the start of a new phase in the war," he warned.

Hezbollah is an ally of Palestinian militant group Hamas, which has been fighting a war in Gaza since its October 7 attack on Israel.

For nearly a year, the focus of Israel's firepower has been on Gaza, which is ruled by Hamas.

But its troops have also been engaged in near-daily clashes with Hezbollah militants along its northern border, killing hundreds in Lebanon, most of them fighters, and dozens in Israel.

The exchanges of fire have forced tens of thousands of people on both sides of the border to flee their homes.

Nasrallah vowed to keep up Hezbollah's fight against Israel until a ceasefire in Gaza is reached.

"The Lebanese front will not stop until the aggression on Gaza stops" despite "all this blood spilt," he said. (AFP)