The Hezbollah leader, Hassan Nasrallah, did not say how his group would respond to attacks on hand-held devices, which killed dozens when pagers and walkie-talkies exploded.

Hezbollah has accused Israel of crossing “all red lines” with its deadly detonation of walkie-talkies and pagers, as Israeli forces launched a fresh wave of strikes across Lebanon. Sonic booms from low-flying Israeli jets shook the buildings in Beirut during a televised speech by the militant group’s leader Hassan Nasrallah in which he warned this week’s unprecedented action “could be called a declaration of war”.

The absence of a full-blown war in Lebanon has been touted as a core U.S. achievement, but now Washington’s grip on the crisis appears more tenuous than ever.

Lebanon and Hezbollah have blamed Israel for the attacks on Tuesday and Wednesday that killed 37 people and wounded around 3,000, although Israel has not directly commented on the attacks, which security sources say were probably carried out by its Mossad spy agency.