The head of Hezbollah said that the use of radios and pagers by members of the Lebanese armed group for bomb strikes "crossed all red lines" and charged Israel with what he believed was a declaration of war.

Hassan Nasrallah gave a much-awaited address in which he admitted that Hezbollah had taken a "unprecedented blow," but he also promised that the organization would keep fighting and exact a "just punishment."

Israel has not said it was behind the blasts on Tuesday and Wednesday, which Lebanese authorities said killed 37 people and wounded 3,000.

As Nasrallah spoke, Israeli warplanes caused sonic booms over Beirut, scaring an already-exhausted population, and others struck targets in southern Lebanon.

The Israeli military said it was operating to “degrade Hezbollah’s terrorist capabilities and infrastructure” and to “bring security to northern Israel”.

Eleven months of cross-border fighting between Hezbollah and Israel sparked by the war in Gaza have killed hundreds of people, most of them Hezbollah fighters, and displaced tens of thousands on both sides of the border.

Hezbollah has said it is acting in support of the Palestinian armed group Hamas. Both are backed by Iran and proscribed as terrorist organisations by Israel, the UK and other countries.

There were no surprises in Hassan Nasrallah’s televised address on Thursday afternoon - his first public reaction to the exploding device attacks which created panic across Lebanon and raised fears of another major war between Hezbollah and Israel.

In what was a humiliating security breach, 12 people were killed, including two children, when pagers used by Hezbollah members to communicate blew up almost simultaneously across the country on Tuesday, according to Lebanon’s health minister. Another 25 were killed when walkie-talkies exploded the next day.

Reports citing Lebanese and US sources said Israeli intelligence operatives were likely to have planted small amounts of explosives inside the devices or their batteries.

“The enemy crossed all rules, laws and red lines. It didn't care about anything at all, not morally, not humanely, not legally,” Nasrallah said.

“This is massacre, a major aggression against Lebanon, its people, its resistance, its sovereignty, and its security. It can be called war crimes or a declaration of war - whatever you choose to name it, it is deserving and fits the description. This was the enemy's intention,” he added.

The Hezbollah leader acknowledged that this was a massive and unprecedented blow for his group, but he insisted that its ability to command and communicate remained intact.

Nasrallah’s tone was defiant and he vowed a harsh punishment. But, again, he indicated that Hezbollah was not interested in an escalation of its current conflict with Israel.

The group’s cross-border attacks, he said, were going to continue unless there was a ceasefire in Gaza, and that no killings or assassinations would return residents to northern Israel.

Shortly before the speech, crowds of Hezbollah supporters gathered in the capital’s southern suburbs to bury two members killed on Tuesday. Some people said they had been shaken by the explosions, but that they were determined to resist.

On Thursday morning, Hezbollah fighters in southern Lebanon fired two anti-tank missiles across the border, followed by drones.

The Israel Defense Forces (IDF) said two Israeli soldiers were killed and a third seriously wounded.

The latest exchanges come at a time when Israel says its military focus has shifted away from Gaza to the situation in the north.

The IDF said on Thursday that its chief of staff, Lt Gen Herzi Halevi, had “recently completed approval of plans for the northern arena”.

Later, at a meeting of military and intelligence chiefs, Israeli Defence Minister Yoav Gallant said: “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,” he added.

“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.”

It is not clear how Israel intends to achieve this goal. But reports earlier this week suggested that the general in charge of the IDF’s Northern Command favoured the creation of an Israeli-controlled buffer zone inside southern Lebanon.

In his speech, Hassan Nasrallah called the general a fool and said that any such move would have dire consequences for Israel.