Israel said it pounded Lebanon's Hezbollah, just hours after the group's leader vowed retribution for deadly explosions that targeted its communication devices, killing 37 people and wounding thousands.

The U.N. peacekeeping force in south Lebanon urged de-escalation on Friday after a big increase in hostilities at the Lebanese-Israeli border, where Israel and the Iran-backed Hezbollah have been trading fire for almost a year.

Bulgaria and Norway became new focal points on Thursday of a global hunt for who supplied Hezbollah with the thousands of pagers that exploded in Lebanon this week in a deadly blow to the militant group.