Hezbollah fired over 100 rockets early Sunday across northern Israel, with some landing near the city of Haifa, as Israel launched hundreds of strikes on Lebanon.
Israel launched hundreds of strikes on Lebanon, targeting militant sites, including rocket launchers, across southern Lebanon.
Hezbollah's deputy leader Naim Kassem declared an "open-ended battle" with Israel, vowing to continue military operations against Israel in support of Gaza.
Rockets hit residential areas in Israel, including a house in Kiryat Bialik, wounding at least three people and setting buildings and cars ablaze.
Israel's Prime Minister Benjamin Netanyahu vowed to take whatever action was necessary to restore security in the north and allow people to return to their homes.
The US has been involved in extensive and quite assertive diplomacy to prevent an all-out war between Israel and Hezbollah.
The Israeli military said it struck about 400 militant sites, including rocket launchers, across southern Lebanon in the past 24 hours, thwarting an even larger attack.
The UN envoy for Lebanon, Jeanine Hennis-Plasschaert, said the region is on the brink of an imminent catastrophe, and there is no military solution that will make either side safer.