It came after back-to-back days of booby-trapped communication devices exploding across Lebanon.

Dozens have been killed - fighters and supporters as well as women and at least two children.

This was the first time his fighting group was to hear from its head after two days of terror and a great deal of shock at the unprecedented method of attack.

Hassan Nasrallah's speeches, broadcast through the Hezbollah television channel, tend to attract thousands in public gatherings, which are a chance for his fervent supporters to demonstrate their loyalty.

The gatherings are usually marked by much cheering and chanting.

Not this time - perhaps because of the security risk after the group's communication network was so demonstrably compromised, there was no large public gathering.

Instead, huddles gathered around televisions in their homes and cafes to listen to what the head of one of the most powerful non-state fighting groups had to say.

Nasrallah himself always delivers his speeches remotely for the same security reasons.

From his secret location, the religious and military leader known for his long, rousing speeches admitted the superiority of Israel's technological ability.

'Unprecedented blow'

He accepted how much of an impact the string of pager explosions and those of hand-held radios had exacted on his outfit - designated a terror group by the US and UK.

He called the explosions "severe" and admitted they'd delivered an "unprecedented" blow to his group.

To his tens of thousands of followers, these are words they probably never expected to hear from their leader, who's spent years boasting of the group's military capabilities and strengths.

In recent speeches, he's told his loyalists how they have a fighting force of more than 100,000 and urged fighters from abroad who wanted to come and join Hezbollah in the war with Israel that they didn't need them.

"We have enough," he's said. "We can do it on our own."

An admission of vulnerability from Hassan Nasrallah is a very rare statement.

And even as the cafes of south Beirut were packed while they listened to the Hezbollah leader vow revenge and "just punishment" against their neighbour, Israeli jets flew low and noisily over the capital, Beirut - at one stage causing sonic booms, setting off car alarms and causing fresh anxiety among an already edgy population.

Hezbollah has launched an internal investigation into how their communications network was so comprehensively infiltrated.

He'd already warned his followers to stop using their mobile phones back in February when the group suspected they were being tracked after several commanders were killed.

'Red lines'

Less surprising was Nasrallah's defiance - a trademark not of his but, it seems, most of his supporters.

He denounced Israel for what he called a massacre that "crossed all red lines", saying civilians were among the victims and the pagers and radios were blown up in a range of public spaces - markets, shops, homes and hospitals.

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And he ominously went on to warn his group would not let the Israelis return their citizens to the north.

In nearly a year of tit-for-tat cross-border attacks since Hezbollah entered the war saying they were supporting the Palestinians in Gaza, thousands of residents in both Israel and Lebanon have been forced out of their communities on either side of the border because of the attacks.

The Israeli prime minister and his defence minister have both vowed to return Israeli citizens to their border homes, with Yoav Gallant declaring a "new phase of the war" - although Israel has not publicly accepted responsibility for the device explosions.

But Hassan Nasrallah indicated that plan is likely to lead to a long and bloody battle.

"No killings, no assassinations, no all-out war can return residents to the border," he vowed.

And that seems to signal there'll be no let-up in the deaths and devastation.

Additional reporting from Beirut with camera Jake Britton, specialist producer Chris Cunningham and Lebanon team Jihad Jneid, Hwaida Saad and Sami Zein