Twenty-one people have been killed and 47 others have been injured in strikes in the eastern part of Lebanon on Sunday, and another 24 people were killed and 29 hurt in an Israeli strike in Ain al-Delb, about 20 miles south of Beirut, according to the Lebanese Ministry of Health.

The Israel Defense Forces said it struck "120 Hezbollah terror targets" in Lebanon on Sunday.

The downbeat mood in Israel following Oct. 7 and throughout much of the conflict in Gaza is now gone, and instead there is "a sense of euphoria," an Israeli official told ABC News.

"National pride is back. We are happy we’ve shown people what we can do," the official said.

Two Israeli officials suggested Israel’s military campaign in Lebanon still has some time to run its course and both of them claimed Israel has now "significantly degraded" Hezbollah’s long- and medium-range missile capabilities.

"I think Hezbollah has got the point," said the second official, who said the recent attacks and the killing of Hezbollah leader Hassan Nasrallah and other senior Hezbollah figures was a "wake-up call" for the Arab world in terms of what Israel can do.

But both officials conceded that Hezbollah does still pose a threat.

The second official said Hezbollah still has "way too much [missile] capability to cause damage to Israel and its civilians."

"We are going to finish the job. We’ve done a lot, but there’s a lot more we can do, and Iran should take note," the official said.

On Iran’s potential response, the second official said, "Our message to them, Iran: Don’t. Because if they do, they’ll be hit harder than they can imagine."

-ABC News’ Tom Soufi Burridge

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