Israel and Hezbollah on Sunday launched their heaviest exchange of fire after months of strikes and counterstrikes, raising fears of an all-out war that could potentially draw in the United States, Iran and militant groups across the region.

By mid-morning, it appeared the exchange of fire had ended, with both sides saying they had only aimed at military targets. Lebanese authorities said the Israeli strikes killed three people, while there were no reports of casualties on the Israeli side. The situation remained tense.

Air France is suspending flights to Tel Aviv and Beirut scheduled for Sunday and Monday after Israel launched massive air strikes into Lebanon and Hezbollah fired rockets and drones at Israel in response to Fouad Shukur's killing, the airline said.

"Flights today and tomorrow are suspended," a spokesman for the French carrier said, adding that the suspension could be extended depending on the situation in the Middle East.

Yemen's Iran-backed Houthi rebels praised attacks by Lebanon's Hezbollah on Israel Sunday and renewed threats to launch their own attack in response to Israeli strikes on a port in Yemen.

"We congratulate Hezbollah and its Secretary-General on the great and courageous attack carried out by the resistance this morning against the Israeli enemy," said a Houthi statement, adding that a response to July 20 strikes by Israel on the rebel-run Hodeida port "is definitely coming."

A spokesman for the U.S. National Security Council, Sean Savett, said Sunday that President Joe Biden was “closely monitoring events in Israel and Lebanon,” after Hezbollah said it fired hundreds of rockets and drones at Israel to avenge Fouad Shukur's killing and Israel said it struck 40 Hezbollah targets in south Lebanon to foil the attack.

“At his direction, senior U.S. officials have been communicating continuously with their Israeli counterparts,” Savett added.

U.N. Special Coordinator for Lebanon Jeanine Hennis-Plasschaert and the U.N. Interim Force in Lebanon (UNIFIL) on Sunday called on Israel and Hezbollah to “cease fire and refrain from further escalatory action,” in light of the “worrying developments across the Blue Line since the early morning.”

Israeli Defense Minister Yoav Gallant announced a 48-hour nationwide state of emergency from 06:00 am (0300 GMT) Sunday, after the Israeli military launched what it called pre-emptive strikes in south Lebanon.

"The declaration on the state of emergency enables the IDF (Israeli military) to issue instructions to the citizens of Israel, including limiting gatherings and closing sites where it may be relevant," Gallant said, in a statement issued by his office.

Israeli Prime Minister Benjamin Netanyahu vowed Sunday "to do everything" to ensure the security of residents of northern Israel after the military launched massive air strikes against Hezbollah targets in southern Lebanon and the Lebanese group said it had avenged the killing of its military chief Fouad Shukur.

"We are determined to do everything to protect our country, return the residents of the north safely to their homes and continue to follow a simple rule: whoever hurts us, we hurt them," Netanyahu said in a statement issued by his office.

Lebanon's health ministry said three people were killed Sunday in Israeli raids in the country's south, after Israel launched strikes against Hezbollah, which announced a wide-scale attack on Israel.

An "Israeli drone strike on a car in the village of Khiam" killed one person, the health ministry said in a statement.

Hezbollah said its chief Sayyed Hassan Nasrallah will speak later Sunday after the Lebanese group announced it had launched a large-scale attack on Israel in response to Fouad Shukur's assassination, and Israeli forces struck Lebanon.

Nasrallah will speak at 6:00 pm (1500 GMT), addressing "the latest developments," a statement from the group said.

Israel launched a wave of airstrikes across southern Lebanon early Sunday in what it said was a pre-emptive strike on Hezbollah, as the group said it had launched hundreds of rockets and drones to avenge the killing of one of its top commanders last month.

The Israeli military said its fighter jets attacked "thousands" of Hezbollah rocket launchers in south Lebanon that were aimed at northern and central Israel.