Israel-Gaza-Lebanon updates: Nasrallah killed for tying Hezbollah cause to Gaza war

Israel decided to assassinate Hezbollah leader Hassan Nasrallah because he refused to separate diplomatic talks on the Hezbollah-Israel front from the war in Gaza, according to an Israeli official.

Nasrallah was killed in an Israeli airstrike on Friday.

The Israeli official said the decision to assassinate Hezbollah's leader was made because Nasrallah declined diplomatic efforts in the last 11 months to separate the "northern front" -- Lebanon -- from the war in Gaza.

The official also said Hezbollah attacks in the last weeks and months had expanded in range and velocity, which “led us to understand that he cannot be part of the game and decision maker in the region anymore.”

The official said it is up to Nasrallah's successor to agree to a diplomatic solution that allows Israel to achieve the goals it has publicly set -- the safe return of over 60,000 Israelis to their homes in the north. However, the official added, Israel has "many other tools to make sure that if they do not agree, we have other ways to achieve" that goal.

Iranian President Masoud Pezeshkian said at a cabinet meeting Sunday that Nasrallah's assassination will not go unanswered, according to Iranian state media.

Hezbollah has confirmed the death of Nabil Qaouk in Beirut, Lebanon, after the Israel Defense Forces said it killed the head of Hezbollah's "preventive security unit" in an airstrike.

Nabil Qaouk was also a member of Hezbollah's Central Council, the IDF said.

The IDF said Qaouk was "considered to be close to the top of the terrorist organization Hezbollah and was directly involved in promoting terrorist acts against the state of Israel and its citizens, even in recent days."

-ABC News' David Brennan

White House National Security spokesman John Kirby said on ABC News' "This Week" that Hezbollah's command structure has been "nearly decimated" and that thousands of the terrorist group's drones and missiles have been destroyed.

"There's no question that the Hezbollah of today is not the Hezbollah that was even just a week ago," Kirby told ABC's Martha Raddatz.

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The Israel Defense Forces said it conducted an airstrike on a school in Gaza, in the northern city of Beit Lahiya, to target "terrorists who were operating inside a Hamas command and control center."

Four people were killed and 15 were wounded, according to Gaza Civil Defense.

The death toll in Gaza since Oct. 7 now stands at 41,595, according to the Gaza Ministry of Health.