Hassan Nasrallah says the exploding device attacks are "a declaration of war" which paid "no heed to innocent people".

Israel launched a series of strikes on Hezbollah targets Thursday as the war against the Lebanon-based group widened in the wake of two consecutive days of deadly explosions triggered in wireless devices.

The attack came as the militant group’s leader said two days of pager and walkie-talkie explosions amounted to a declaration of war.

Hezbollah leader Hassan Nasrallah in a speech broadcast said the attacks "could be considered war crimes or a declaration or war."

Israel Defense Forces on Thursday said it carried out strikes on multiple infrastructure sites where Hezbollah operates in southern Lebanon. (Credit: Israel Defense Forces)

More than 20 people, including at some children, have been killed after pagers and walkie talkies exploded, Lebanon says.

But his keenly-awaited address was disrupted by the sound of sonic booms from low-flying Israeli jets ringing across the Lebanese capital. Minutes before he began, the IDF confirmed it had also struck a series of Hezbollah targets in southern Lebanon.