Iran and its proxies are vowing to punish Israel for the apparent assassination of top Hamas political leader Ismail Haniyeh in Tehran, bringing the two countries closer to an all-out war in the Middle East. 

Israel, which has not acknowledged the strike in Iran, said one of its primary goals in the war against Hamas is the death of its top leaders, including Haniyeh. 

But Haniyeh’s death on Iranian soil, just more than three months after Iran directly fired at Israel with hundreds of missiles and drones in an unprecedented attack, is a major escalation in the already spiraling conflict across the Middle East. 

It also comes just one day after Israel killed the top military leader of the Iranian-backed Hezbollah militant group in Lebanon’s capital of Beirut, where war has been threatening to break out for months. 

Aaron David Miller, a senior fellow at the Carnegie Endowment for International Peace, said the risk of a regional war is growing, which he speculated would begin with a larger Israeli-Hezbollah conflict. 

“It would evolve into Iranian involvement because Iran could not stand by and see [Hezbollah] decimated by the Israelis,” he said of a wider war. “I don’t think we’re going there. I think where this is probably heading is a series of episodic confrontations, which could get pretty intense.” 

Asher Kaufman, professor of history and peace studies at the University of Notre Dame, said that “by targeting these two top leaders, the Israeli government demonstrated that it is willing to take the risk of a full war.” 

“We are certainly closer to a downward spiral today than we were yesterday,” Kaufman said in an email. “It seems like all parties, including Israel, are not interested in a full-scale war, but at the same time, all continue to inch forward toward that possibility. The Middle East is by far in a moment of extreme fragility and uncertainty about the future.” 

Iran’s Supreme Leader Ayatollah Ali Khamenei promised a “harsh punishment” for the Wednesday strike that killed Haniyeh and his bodyguard at his residence while he was in Tehran to attend the inauguration of the newly elected Iranian president. 

​​“Following this bitter, tragic event which has taken place within the borders of the Islamic Republic, it is our duty to take revenge,” Khamenei said on social platform X. 

Khamenei, later on Wednesday, ordered his forces to respond, according to The New York Times. 

Hamas and other Iranian-backed groups, including Hezbollah in Lebanon and the Houthis in Yemen, also quickly condemned Israel for the killing of Haniyeh and vowed retaliation for the attack.  

The Haniyeh strike showed the vast capabilities of Israeli intelligence and exposed a weakness in Tehran to defend the nation, putting pressure on Iran to respond with strength. 

But experts say Tehran does not likely have the resources or appetite for another massive attack on Israel like it did in April. That attack followed the death of several members of Tehran’s paramilitary group Islamic Revolutionary Guard Corps, which Israeli forces struck near the Iranian Embassy in Syria. 

Instead, Iran may respond through its proxies. The most likely attack will come from Lebanon, where Hezbollah has been firing artillery and rockets at Israel for nearly 10 months in a campaign tied to the Israeli war against Hamas in Gaza. 

Hezbollah may already be weighing a response after a Tuesday Israeli strike in Beirut killed Fuad Shukr, the right-hand man and principal military adviser to Hezbollah’s leader, Hassan Nasrallah. That Israeli strike came in response to a Hezbollah rocket attack on a soccer field in Israel that left 12 children and teenagers dead. 

Still, Iran may not want to risk Hezbollah, its most star proxy, in a larger fight with Israel, especially as Tehran has sought to avoid a wider war to preserve its proxies as a bulwark against Israel. Other possibilities for Iranian retaliation include a one-off strike or targeted assassination of an Israeli official. 

Gene Moran, a national security expert and retired U.S. Navy destroyer captain, said he expects Iran to respond directly and that the outcome could be far different than the April attack, which saw Israel and allied forces completely defeat an Iranian flurry of drones and rockets. 

“This is an issue of sovereignty in Tehran,” said Moran, now an adjunct professor at Florida State University. “My first thought on seeing that [Israel] made an attack in Tehran was that this is the ultimate, ‘I can come put my feet up on your coffee table anytime I want,’ sort of message, and that’s just not going to be well received.” 

The U.S. and Israel are likely preparing for a potential response by moving assets and forces across the region and by ramping up intelligence gathering. In the event of a large attack on Israel, the U.S. is expected to help defend its ally. When Iran attacked in April, U.S. forces, along with Arab nations in the region, stepped in to defend Israel. 

U.S. Defense Secretary Lloyd Austin told reporters Wednesday that the U.S. “certainly will help” Israel if it is attacked. 

“You saw us do that in April. You can expect to see us do that again,” Austin said. “But we don’t want to see any of that happen.” 

Israel’s war against Hamas in Gaza has devastated the group responsible for a deadly Oct. 7 attack that killed about 1,200 people in southern Israel. Hamas also took some 250 hostages. 

Hamas has lost thousands of fighters in the war, which has killed more than 39,000 people in Gaza, according to health authorities that do not distinguish between fighters and noncombatants.  

Over the course of the war, Israel has targeted dozens of Hamas leaders and in June may have killed the top military commander, Mohammed Deif, though his death is not confirmed. Top Hamas Gaza leader Yahya Sinwar remains at large.  

Killing Haniyeh is the largest blow yet to Hamas, which is unlikely to be able to respond with any meaningful might after losing its strength in Gaza. 

Israeli Prime Minister Benjamin Netanyahu appeared to take a victory lap Wednesday, saying in a video address he has achieved significant results in the war despite pressure to end the conflict. 

“We’ve achieved all of that over the past few months because we did not surrender, because we have reached some very brave decisions despite very heavy pressures from within and without,” he said. 

Avi Melamed, a former Israeli intelligence official, said Israel was “raising the stakes” by targeting Haniyeh on Iranian soil. 

“They’re basically saying to the Iranians we are willing, able and ready for any kind of [conflict] but now we are taking the lead, now we are taking control,” he said of Israeli thinking. “We are the ones reshuffling the cards of the game.” 

Haniyeh’s death and any Iranian or proxy response is likely to be a major setback for negotiations to reach a cease-fire in Gaza and release the remaining 116 hostages — about 44 considered dead — still held in the territory.   

The U.S., which said it was not involved in the strike on Haniyeh, is continuing to reiterate its calls for a cease-fire and hostage release deal, even after the attacks in Beirut and Tehran.  

White House national security spokesperson John Kirby told reporters Wednesday that the Israeli strikes in Lebanon and Iran complicate the negotiations. 

“These reports over the last 24, 48 hours certainly don’t help with the temperature going down,” Kirby said. “It certainly doesn’t make the task of achieving that outcome any easier.” 

Sina Azodi, a visiting scholar and lecturer on international affairs at George Washington University, said the developments don’t necessarily “kill” the prospects of a cease-fire deal. 

“But it will significantly jeopardize the possibility of reaching a cease-fire,“ he said, “because it really ties the hands of anyone who would be interested in giving any concessions to the Israelis at the time where the political leadership was just assassinated by the Israelis.”