Israeli military said on Monday it was striking targets of the Iran-backed Hezbollah terrorists across Lebanon, after the group launched missiles and drones towards Israel in retaliation for the killing of Iran's Supreme Leader Ali Khamenei.

The projectiles launched by the Lebanese terrorist group were the first since the start of U.S. and Israeli strikes on Iran.

The Shi'ite Muslim group, long one of Tehran's principal allies in the Middle East, said it launched the attack against Israel in response to Israel killing Khamenei and continuous Israeli violations against Lebanon.

"The resistance leadership has always emphasized that the continuation of Israeli attacks and the assassination of our leaders, youth, and people gives us the right to defend ourselves and respond at the appropriate time and place," Hezbollah said in a statement.

"The IDF (Israel Defense Forces) will operate against Hezbollah's decision to join the campaign, and will not enable the organization to constitute a threat to the State of Israel," the military said.

Explosions were heard in the Lebanese capital Beirut, according to witnesses. Lebanese security sources told Reuters that Israel had struck Beirut's southern suburbs, a Hezbollah stronghold.

Israel and Lebanon agreed to a U.S.-brokered ceasefire in 2024, ending more than a year of fighting between Israel and Lebanese militant group Hezbollah that had culminated in Israeli strikes that severely weakened the Iran-backed group. Since then, the sides have traded accusations over violations.

Lebanon's presidency said on Saturday it had been told by the U.S. ambassador that Israel would not escalate against Lebanon as long as there are no hostile acts from the Lebanese side.