Israel-Gaza-Lebanon updates: IDF orders evacuations in Beirut as huge blast hits city

The Iranian regime is unlikely to take direct military action against the U.S. homeland following Israel's killing of Hezbollah leader Hassan Nasrallah, though his death could prompt Iran or its proxies to take alternative actions like cyberattacks, according to a new Department of Homeland Security alert.

Nasrallah's death is also unlikely to galvanize people within the U.S to take action, though the "expansion of the regional conflict and potential for increased circulation of graphic images highlighting civilian deaths could contribute to [extremist] radicalization to violence,” according to the Sept. 30 document obtained by ABC News and distributed to law enforcement agencies around the country.

"We also assess that it is unlikely that Iran or its proxies will target the homeland during any potential physical response to the airstrike,” the alert stated. "We are concerned that the incident may prompt Iranian government or other malicious cyber actors supportive of Tehran's interests to conduct cyber attacks against poorly secured US critical infrastructure entities, among other targets."

-ABC News' Aaron Katersky and Josh Margolin

Israel will have a "significant response" to Iran's attack, an Israeli official told ABC News.

"What Iran has suffered so far is only a promo," the official said.

-ABC News' Jordana Miller

The Israeli military does not see any additional threats at this time from Iran, Israel Defense Forces spokesperson Rear Adm. Daniel Hagari said.

Hagari said they have carried out a "large number of interceptions." There were a "few hits" in the south and officials are assessing the damage, though there are no reported casualties, he added.

"We are on high alert both defensively and offensively," he said. "We will defend the citizens of the State of Israel. This attack will have consequences."

The U.S. was involved in the effort to intercept some of the Iranian missiles launched against Israel, an official told ABC News.

"In accordance with our ironclad commitment to Israel’s security, U.S. forces in the region are currently defending against Iranian-launched missiles targeting Israel," the official said. "Our forces remain postured to provide additional defensive support and to protect U.S. forces operating in the region."

-ABC News' Matthew Seyler