Israel and the US prepare for 'series of scenarios,' including a potential Hezbollah attack

TEL AVIV -- The Israeli military is working in close coordination with the Pentagon to prepare for a "series of scenarios" in which either Iran or one of its proxies, namely Hezbollah, could launch an attack or series of attacks against Israel, an Israeli defense official told ABC News.

Both Iran and its Lebanese proxy group, Hezbollah, have vowed to take revenge against Israel for two assassinations carried out in Beirut and Tehran last week, which killed Fuad Shukr, a senior Hezbollah commander, and Hamas political leader Ismail Haniyeh, respectively. Israel has not claimed responsibility for Haniyeh's death.

The Israeli official, who spoke with ABC News on condition of anonymity, suggested one red line for Israel, which could ratchet up tensions, would be an attack that harms or targets Israeli civilians.

"We don't have an interest in a war or escalation," the Israeli defense official said. "But we won't tolerate attacks on our citizens."

The defensive preparations being made by Israel in conjunction with the United States were "very critical," the official said.

"What we are seeing is the U.S. taking a very clear position in their actions and their messaging, and it matters," the Israeli defense official told ABC News.

In the wake of the assassinations, the Pentagon has announced it is moving two additional naval destroyers and a squadron of F-22 Raptor fighter jets into the Eastern Mediterranean as part of efforts to bolster defenses in and around Israel.

In an unusual step, U.S. officials also said a squadron of F-18 fighter jets from the aircraft carrier USS Theodore Roosevelt were being redeployed to an undisclosed airbase in the Middle East.

The Israeli defense official said these redeployments of American military assets, which were aimed at defending Israel, appeared to be "unprecedented" in scale and scope.

'Steeper hurdle' with regional allies

The Biden administration has also been talking to regional allies about efforts to defend Israel from a potential Iranian attack.

However, U.S. diplomats told ABC News earlier this week they were "facing a steeper hurdle" convincing partners in the region to rejoin the defensive coalition, which rallied to protect Israel from attacks by more than three hundred Iranian drones and missiles back in April.

Many international partners see "some of Israeli Prime Minister Netanyahu's actions – particularly the killing of Hamas political leader Ismail Haniyeh in Iran – as unnecessarily provocative," two U.S. officials familiar with the matter told ABC News earlier this week.

Although Israel has not claimed responsibility for Haniyeh's death, neither has it denied that it carried out the assassination in the Iranian capital. Israel did claim responsibility for the strike on Beirut that killed Fuad Shukr.

Iran's Revolutionary Guard said in a statement released on Saturday that Israel would face "severe punishment" for the assassination, which they said would come at an appropriate time and place.

'A fine balance'

Two former Israeli generals told ABC News they believed that if Iran attacks, that attack would likely be of a different type than the missile and drone barrage in April, which proved largely ineffective. Iran gave Israel and its allies hours of warning that the April attack was imminent. Analysts agree that there is not likely to be the same degree of warning ahead of any future attack.

"This time they must do something different … something that will cause a much more painful price," former Israeli Gen. Yossi Kupperwasser, who was in charge of the Research Division at the Israel Defense Forces' (IDF) Intelligence Corps, told ABC News.

Kupperwasser said the delayed response from Iran was partly because the Iranians wanted "to be sure that they are going to be successful." However, he noted, Iran also had to consider Israel's potential response to any attack.

"[The Iranian government] knows they are vulnerable. If Israel decides to retaliate then it can cause very painful damage. The Iranians have to take this into account," the former general told ABC News.

According to Meir Javedanfar, a lecturer and senior research fellow at Israel's Lauder School of Government, Diplomacy and Strategy, the Iranian leadership faces a very delicate balancing act. Though Tehran has vowed it will act and will want to be seen to do something to deter Israel from future hostile acts, Iran cannot afford to hit Israel too hard and provoke a more potent response, he said.

"They know they need to get this right," Javedanfar told ABC news. "It is a fine balance."

Retired Israeli Major Gen. Amos Yadlin, who is now president and founder of the nonprofit national security consultancy MIND Israel, echoed that sentiment, telling ABC News that in a sense, Israel, Iran, and Iran's proxy in Lebanon, Hezbollah, all face the same dilemma: calibrating their attacks so that they are effective, while trying to ensure they are not too effective, in a way that could lead to a broader conflict.

"They all want to achieve the goal of retaliation and deterrence [with their attacks]. However, none of them want to reach a full-scale war," Yadlin said.

Hezbollah under 'more pressure' than Iran to act

On Tuesday, the leader of Hezbollah, Hassan Nasrallah, said his group would respond to the Israeli airstrike in Beirut on July 30, which killed Fuad Shukr.

The same Israeli defense official who told ABC News of the joint U.S.-Israeli preparations for a potential Iranian or Hezbollah attack further said that Israel's July 30 attack in southern Beirut was "a direct response" to a rocket attack on July 27 in Majdal Shams, in the Israeli-controlled Golan Heights, which killed 12 children and teenagers – an attack for which Israel blames Hezbollah.

"Hezbollah crossed a red line," the defense official said.

Yadlin, who for five years was in charge of Israeli military intelligence, said Hezbollah "is under more pressure than Iran to act."

Hezbollah "lost the top military leader and they are trying to bring a clear red line that an attack on Beirut is unacceptable," he added.

Yadlin predicted Iran might wait longer to respond to the assassination of Hamas leader Ismail Haniyeh, who was killed in an explosion the early hours of Aug. 31 in Tehran. Three Middle Eastern sources have previously told ABC News that Haniyeh was killed by a bomb, planted in his room in the Revolutionary Guard guesthouse, where he was staying for the inauguration of Iran's new president.

Yadlin told ABC News that the fact that it was a Palestinian leader killed in Tehran, and that he was not killed by a missile fired from outside of the country, gave Tehran some wriggle-room in its response.

"I see them waiting," Yadlin said.

ABC News' Jordana Miller, Luis Martinez and Becky Perlow contributed to this report.