Hezbollah's leader said this week's two deadly attacks on the Lebanon-based militant group's pagers and walkie-talkies is a "declaration of war".

Hassan Nasrallah admitted the two-day attack, which killed at least 37 and wounded thousands, was a "severe blow" and warned that Israel had crossed a "red line".

As Nasrallah spoke in a televised address from an unknown location, Hezbollah and the Israeli military traded new strikes over the border.

"Yes, we were subjected to a huge and severe blow," Nasrallah said of the attack widely believed to be carried out by Israel's spy agency on communications devices which exploded in faces of Hezbollah members, even crippling or blinding some fighters.

"The enemy crossed all boundaries and red lines," he added.

Israeli war planes flew low over Beirut and broke the sound barrier during the speech creating huge 'sonic booms' that shook the city.

The Israeli military had launched air strikes on southern Lebanon overnight.

Meanwhile two Israeli soldiers were killed in combat on Thursday in the north of Israel.

Israel's N12 News said one of them was killed by a drone and the other by an anti-tank missile fired by Hezbollah across the Lebanese border.

As usual, Nasrallah spoke by video from an undisclosed location.

Hezbollah typically convenes a rally for supporters to watch his speeches on a big screen, but this time they did not.

There is no doubt "we've been breached", he said before adding Israel tried to kill 5,000 in two minutes and that the blasts were unprecedented in the history of both Lebanon and the world.

Nasrallah called the device attacks "a declaration of war" and says Israeli prime minister Benjamin Netanyahu's military paid "no heed to innocent people".

Turning to how Hezbollah intends to respond, Nasrallah said. "In the name of all those who've lost martyrs, who were injured, in the name of all those who've fought in the name of Gaza, we tell Netanyahu and Gallant, to the enemy, that the Lebanese front will not stop before the aggression in Gaza stops.

"The resistance in Lebanon will not stop supporting the people of Gaza and the West Bank."

An investigation into how it happened has been launched, he added.

He said: "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."