The escalation comes as Lebanon is still recovering from the explosion of thousands of pagers and radios across the country in what has been widely accepted as an Israeli attack that spanned two days this week. Israel has yet to comment on the attacks.

Speaking for the first time since the deadly device sabotage, Hezbollah leader Hassan Nasrallah vowed on Thursday that Israel would face retribution.

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

As he delivered his address, Israeli fighter jets roared over Beirut, their sonic booms shaking buildings and sending residents scrambling for cover.

Hours later, Israel's military claimed its jets hit "approximately 100 launchers...consisting of approximately 1,000 barrels" set to be fired immediately.

Lebanon's state-run National News Agency said Israel struck the south at least 52 times. It was one of the heaviest Israeli bombardments of south Lebanon since the border exchanges erupted last October.

Hezbollah meanwhile said it launched at least 17 attacks on military sites in northern Israel.

The device blasts and Thursday's barrage of air strikes came after Israel announced it was shifting its war objectives to its northern border with Lebanon where it has been trading fire with Hezbollah.

For nearly a year, Israel's firepower has been focused on its deadly assault on Gaza, but its troops have also been engaged in near-daily exchanges with Hezbollah fighters.

International mediators have repeatedly tried to avert a full-blown war between Israel and Hezbollah and staunch the regional fallout of Israel's war on Gaza.

Hezbollah maintains its fight is in support of Hamas and Palestinians in Gaza, and Nasrallah vowed the attacks on Israel will continue as long as Israel's assault that has killed thousands of Palestinians and reduced Gaza to rubble lasts.

The cross-border exchanges of fire have killed hundreds in Lebanon, most of them fighters, and dozens in Israel, including soldiers. Tens of thousands of people on both sides of the border have been forced to flee their homes.

Speaking to Israeli troops on Wednesday, Israeli Defence Minister Yoav Gallant said: "Hezbollah will pay an increasing price" as Israel tries to "ensure the safe return" of its citizens to areas near the border.

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

'Wider war'
 

Foreign Minister Abdallah Bou Habib said the "blatant assault on Lebanon's sovereignty and security" was a dangerous development that could "signal a wider war".

Speaking ahead of a UN Security Council meeting on the attacks set for Friday, he said Lebanon had filed a complaint against "Israel's cyber-terrorist aggression that amounts to a war crime".

Iran's Revolutionary Guards said Israel faces "a crushing response from the resistance front" after the blasts, which wounded Tehran's ambassador in Beirut.

US Secretary of State Antony Blinken, who has been scrambling to salvage efforts for a Gaza ceasefire and captive release deal, called for restraint by all sides.

"We don't want to see any escalatory actions by any party" that would endanger the goal of a ceasefire in Gaza, he said as he joined European foreign ministers in Paris to discuss the widening crisis.

Press Secretary Karine Jean-Pierre said President Joe Biden still believes a diplomatic solution between Israel and Hezbollah is "achievable".

Palestinian president Mahmoud Abbas, in Madrid, called for a new peace conference aimed at ending the Israeli-Palestinian conflict.

Israel's relentless bombardment and ground invasion has killed at least 41,272 people in Gaza, most of them women and children, according to the territory's health ministry. The UN rights office confirms most of the dead are women and children

In the latest Israeli episode of violence, the territory's civil defence agency said an air strike on a house in Nuseirat refugee camp killed eight people. Another six people, including children, were killed in a separate strike on an apartment in Gaza city, it added.

In Lebanon, the influx of so many casualties following the blasts overwhelmed medics and triggered panic.

"What happened in the last two days is so frightening. It's terrifying," Lina Ismail told AFP by phone from the eastern city of Baalbek.

"I took away my daughter's power bank and we even sleep with our mobile phones in a separate room," she added in a trembling voice.

'Sabotaged at source'
 

The preliminary findings of a Lebanese investigation found the pagers had been booby-trapped, a security official said.

The country's mission to the United Nations concurred, saying in a letter that the probe showed "the targeted devices were professionally booby-trapped... before arriving in Lebanon, and were detonated by sending emails to the devices".

A source close to Hezbollah, asking not to be identified, said the pagers were recently imported and appeared to have been "sabotaged at source".

The New York Times reported Wednesday that the pagers that exploded were produced by the Hungary-based BAC Consulting on behalf of Taiwanese manufacturer Gold Apollo. It cited intelligence officers as saying BAC was part of an Israeli front.

A government spokesman in Budapest said the company was "a trading intermediary, with no manufacturing or operational site in Hungary".

*This story was edited by Ahram Online.