For 32 years, Hassan Nasrallah led the Lebanese militant group Hezbollah through conflict, growth, and rising tension.
On Friday evening, , and there are growing fears of an all-out war between Hezbollah and Israel that could engulf the Middle East.
"I'm gravely concerned by the dramatic escalation of events in Beirut in the last 24 hours," United Nations secretary general Antonio Guterres wrote on X on Saturday.
"This cycle of violence must stop now. All sides must step back from the brink.
"The people of Lebanon, the people of Israel, as well as the wider region, cannot afford an all-out war."
Lebanon's government has declared three days of mourning while Iran, which arms and finances Hezbollah, has warned the assassination will not go unavenged.
"We warn the leaders of the occupying regime that the unjust bloodshed... especially of Hezbollah's secretary general, martyr Seyyed Hassan Nasrallah, will bring about their destruction," Iran's ISNA news agency quoted Iran's first vice president, Mohammad Reza Aref, as saying.
But as Israel continues hitting Lebanon with strikes, some experts say Hezbollah will likely step back and recalibrate before making major moves.
What does Nasrallah's death mean for Hezbollah?
Israel's escalating conflict with Hezbollah comes against the backdrop of the former's near year-long war with Hamas — the militant rulers of the Palestinian enclave Gaza and an ally of the Lebanese group.
Israel and Hezbollah have been engaged in mostly low-level conflict since the Hamas-led October 7 assault on southern Israel in which militants killed 1,200 people, according to Israeli tallies, and took about 250 others hostage.
That attack sparked the war and Israel's bombardment of Gaza in which more than 41,000 Palestinians have been killed, according to the local health ministry, and plunged the enclave into a deep humanitarian crisis.
But over the past two weeks, conflict between Israel and Hezbollah has ramped up. Lebanese health authorities say more than 1,000 people have been killed, 6,000 wounded, and 200,000 displaced as a result of Israeli strikes.
Earlier this month, used by exploded, killing at least 39 people and wounding about 3,000 in Lebanon.
As well as Nasrallah, Israel's military said it has killed eight of Hezbollah's nine most senior military commanders this year, mostly in the past week.
And, Iran said a senior member of its was killed in the same strike that killed Nasrallah.
Hassan Nasrallah addressed the public in response to a large-scale attack, attributed to Israel, involving the explosion of wireless devices targeting Hezbollah fighters. Source: ABACA / Basili Sandro/ABACA/PA
"I think they will do what they usually do, which is to withdraw and regroup and reorganise and rethink a strategy," she said.
"I don't think they will wage a full war on Israel, that's my opinion as an analyst — but I think that there are different opinions and views on this issue."
Hezbollah has shown the ability to replace commanders quickly, and Nasrallah's cousin Hashem Safieddine has long been tipped as his successor.
Will Nasrallah's death spark an all-out war?
Before the strike on Nasrallah, three Iranian sources told the Reuters news agency Iran was planning to send additional missiles to Hezbollah to prepare for a prolonged war.
Meanwhile, Israel has shot down a proposal for a 21-day ceasefire and its military said it was preparing for a potential ground invasion of Lebanon.
Before Nasrallah's killing was confirmed, Israeli Prime Minister Benjamin Netanyahu told the United Nations General Assembly in New York on Friday (local time) there was .
Alam Saleh, a senior lecturer in international relations at The Australian National University, said Hezbollah is not likely to launch a counterattack in the short term.
"Hezbollah needs to recalculate its own strength and the losses, the damages that it has received," he said.
"However, in the long term, they will come back perhaps more determined to fight against Israel."
Saleh said the strategy of Hezbollah and Iran will be to keep Israel under pressure without escalating into full-scale war.
He said they would seek to undermine Israel's military, political and economic abilities.
"Iran and Hezbollah's strategy is not to defeat Israel, they cannot ... but their strategy is to frustrate Israel, and to diminish its economy and political power.
"They don't need to do much, they just need to not get defeated.
"However, when it comes to Israel, they need to defeat, diminish and annihilate Hezbollah, which they cannot do."
What does it mean for Lebanon?
Hezbollah is a Lebanese Islamist political party and militant group formed in 1982 after Israeli forces invaded southern Lebanon that year.
It leads a multi-party alliance that holds just under half the seats in Lebanon's parliament. Hezbollah makes no distinction between its political and military wings.
Laachir noted due to Hezbollah being embedded in Lebanon's social and political structure, Nasrallah's death would likely have significant impact on the country.
"This is really a huge, worrying development ... Lebanon is almost on the verge of collapse economically, socially and politically," she said.
"They've been dysfunctional for a long time as a state [and] I think this further escalation and flattening of the south of Lebanon, and the continuous attack and bombardment of the rest of country, is really instigating the trauma of the Civil War for the Lebanese people and creating a lot of anxiety and worry."
Laachir said while she does not expect Hezbollah will immediately escalate conflict or counterattack, many people in Lebanon would be afraid of the possibility of more violence.
"I think from the perspective of the Lebanese people — particularly the Shia population, who now feel absolutely exposed — they feel that they don't have protection," she said.
"I think in the wider region, in the surrounding countries for the Egyptians and the Jordanians and other people in the region, I think they're terrified that this war might escalate and create more havoc."
Is it possible for the conflict to be resolved?
Saleh said in order for the wider conflict and ongoing Hamas-Israel war to be resolved, should be accepted.
"Israel should accept this, , and come to a diplomatic agreement with Palestinians — something which evidently Prime Minister Netanyahu and his ministers are not willing to do," he said.
"Israel needs to choose between sustainable peace according to international law and the United Nations' and the international society's demand, or to keep fighting."
Saleh said he believes military power and violence will not solve territorial disputes.
"The fact that they do material damages to others like Gaza and Hezbollah is not necessarily a victory," he said.
"I think the politicians should seek a peaceful end without using coercive means. Diplomatic means are still there and Israel cannot continue this forever."
Laachir said if the United States cuts support and funding to Israel, it could have a significant impact.
"The US needs to take a genuine active role and stop unconditionally supporting Israel," she said.
"They're the only ones who can really reign in Israel; if it carries on it will be catastrophic on all fronts."
With additional reporting by the Reuters news agency.
