Israel announced on Saturday that its forces have killed Hassan Nasrallah, the powerful leader of the Lebanese militant and political group, Hezbollah, in what would mark a major escalation amid mounting hostilities at its northern border with Lebanon.

An Israeli official said Friday that Israeli forces had targeted Nasrallah, who has led the Iran-backed militant group for the past three decades, in a large-scale attack on a suburb of southern Beirut.

“Hassan Nasrallah will no longer be able to terrorize the world,” the Israel Defense Forces said in a post on X.

Hezbollah had yet to confirm whether Nasrallah, 64, had been killed as of early Saturday morning and NBC News was not immediately able to independently verify the claim.

Earlier on Friday, a Hezbollah spokesman had said Nasrallah, who was seldom seen in public, was not in one of the buildings struck by Israeli forces and was “fine.” It was not clear whether that analysis had changed.

Under Nasrallah’s leadership, Hezbollah became the most powerful Iran-backed paramilitary group in the Middle East with an arsenal of ballistic missiles trained on Israel, as well as a potent political player in Lebanon. The disciplined force has also trained other Iran proxies in the region, and fought in Syria to quell forces trying to oust the regime of President Bashar al-Assad.

He called for the “liberation” of Jerusalem, referring to Israel as the “Zionist entity” and lauded Hamas’ Oct. 7, 2023 attacks on Israel as a “heroic, great, and grand operation.”

Hezbollah’s ongoing rocket and drone campaign targeting northern Israel that began soon after, was carried out in solidarity with Palestinians, Nasrallah had said. Hezbollah has vowed to continue its campaign against Israel until it ends its nearly yearlong offensive in Gaza.

Nasrallah was born into a poor Shiite family in Beirut in 1960 and was raised in the Karantina district. He studied theology and after civil war broke out in Lebanon, he joined the Amal Movement, a Lebanese Shia political and paramilitary organization with ties to Iran.

Nasrallah had traveled to Najaf in Iraq, one of the holiest cities in Shia Islam, where he studied at a seminary, before returning to Lebanon and becoming a commander for Amal in Beqaa.

He would later become a founding member of Hezbollah, joining the year the group was formed in 1982 following Israel’s invasion of Lebanon, which began on June 6 of that year.

Hezbollah was formed that year to fight against invading Israeli forces, with Nasrallah rising up to become the secretary-general of the group after his predecessor, Sayyed Abbas Musawi, was killed by Israeli forces in 1992, according to The Associated Press.

Under his leadership, Hezbollah, whose name means “Party of God” and is designated a terrorist organization by the U.S., rose to prominence as it fought to drive Israel from Lebanon until the country withdrew its forces in May 2000.

And his status was further elevated after he led the group in a 34-day war with Israel in 2006 that ended with a United Nations-backed cease-fire. That conflict began when Hezbollah fired rockets at Israeli military bases and border villages and then captured two Israeli soldiers.

Ed Husain, a senior fellow at the Council on Foreign Relations with a focus on the Middle East, said Israel taking aim at Nasrallah could be seen as “a proactive strategy to defend Israel” and should not come as a surprise.

“Israel no longer seems to fear clashing head-on with Iran,” Hussain said, adding, “Israel will not fear entering a larger operation.”

The IDF’s claim of having assassinated Nasrallah came after its forces on Friday launched airstrikes on what it described as Hezbollah’s central headquarters, which they said was located under residential buildings in Dahieh, a southern suburb of Beirut known to be a Hezbollah stronghold.

The assault shook the capital, sending thick plumes of smoke over the city. An NBC News crew witnessed the explosion near the Beirut–Rafic Hariri International Airport.

According to the Lebanese Health Ministry, at least six people were killed 91 injured in the attack targeting Nasrallah, though the damage is extensive and it is possible the official death toll will rise.

Both Lebanese Prime Minister Najib Mikati and Israeli Prime Minister Benjamin Netanyahu returned early from the U.N. General Assembly meeting in New York following news of the attack, following a speech from Netanyahu on Friday defending Israel’s actions in the Gaza Strip and Lebanon as he cast Iran as an enemy against Israel’s wider regional interests.

“There is no place in Iran that the long arm of Israel cannot reach,” Netanyahu said. “And that’s true of the entire Middle East.”

In a statement following the attack, an Israeli official told NBC News the country expected Hezbollah to attempt to mount a major retaliatory attack.

The concern now is an escalation of war in the Middle East, including an Israeli ground operation in Lebanon, which would be “an error in judgment,” Hussain warned.

“Better to succeed using new technology and tactics and avoid old rules of invasion because that is a tried and tested method of failure in Lebanon based on previous attempts,” he said. 

Washington has pushed, alongside a number of allies, for a 21-day cease-fire proposal that would allow for negotiations between Israel and Hezbollah in the hopes of preventing an all-out war.

Husain said he believed the Biden administration, which said it had no prior knowledge of Israel’s plans for the attack targeting Nasrallah, would likely make attempts to “hold back Israel,” but he said he believed it must first address “the arsenal of weapons held by Hamas and Hezbollah.”

“In the absence of removing Hezbollah’s military capabilities, or at least promising to contain Hezbollah, I doubt Israel can be reined in by the U.S. government,” Husain said.