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.

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

At least 12 people were killed, including an 11-year-old boy and a 9-year-old girl, and more than 2,700 people injured in the coordinated explosions of pagers that belonged to Hezbollah members. A day later,