Israeli Prime Minister Benjamin Netanyahu said Israel “will exact a very heavy price from any aggression against us on any front” but did not mention the killing. “There are challenging days ahead,” he added.

Israel had pledged to kill Ismail Haniyeh and other Hamas leaders over the group’s Oct. 7 attack on southern Israel that sparked the war in Gaza. The strike came just after Haniyeh had attended the inauguration of Iran’s new president in Tehran — and hours after Israel targeted a top commander in Iran’s ally Hezbollah in the Lebanese capital, Beirut.

In a statement on his official website, Iranian supreme leader Ayatollah Ali Khamenei said revenge was “our duty” and that Israel had “prepared a harsh punishment for itself” by killing “a dear guest in our home.”

Haniyeh’s killing also could prompt Hamas to pull out of negotiations for a cease-fire and hostage release deal in the 10-month-old war in Gaza, which U.S. mediators had said were making progress.

Israel carried out a rare strike Tuesday evening in the Lebanese capital that it said killed a top Hezbollah commander allegedly behind the rocket strike. Hezbollah, which denied any role in the Golan strike, confirmed the death of Fouad Shukur on Wednesday, saying he was in the building that was hit. The strike also killed three women and two children, according to the Lebanese Health Ministry.

White House national security spokesman John Kirby said there was “no sign that an escalation is imminent” in the Middle East and that a cease-fire agreement for Gaza was still possible. He also said the U.S. could not independently confirm reports of what occurred in Tehran. A key question is whether Israel told the U.S., its top ally, ahead of time.

Asked about Haniyeh’s killing, U.S. Secretary of State Antony Blinken said, “This is something we were not aware of or involved in.” Speaking to Channel News Asia, Blinken said he would not speculate about the impact on cease-fire efforts.

The U.N. Security Council held an emergency meeting Wednesday to discuss the strikes, but it appeared unlikely that the council would coalesce around any message. The United States, a key ally of Israel, and Russia, which has close ties with Iran, are both council members with veto power.

Khalil al-Hayya, a powerful figure within Hamas who was close to Haniyeh, told journalists in Iran that whoever replaces Haniyeh will “follow the same vision” regarding negotiations to end the war — and continue in the same policy of resistance against Israel. Hamas’ main consultative body was expected to meet soon, likely after Haniyeh’s funeral Friday in Qatar, to name a successor.

U.S. Secretary of Defense Lloyd Austin said he still had hopes for a diplomatic solution on the Israeli-Lebanon border. “I don’t think that war is inevitable,” he said. “I think there’s always room and opportunity for diplomacy, and I’d like to see parties pursue those opportunities.”

Israel often refrains from commenting on assassinations carried out by its Mossad intelligence agency or strikes on other countries.

In a statement by his office, Israeli Defense Minister Yoav Gallant said Israel doesn’t want war after its strike on the Hezbollah commander in Beirut, “but we are preparing for all possibilities.” He did not mention the Haniyeh killing, and a U.S.-provided summary of his call with Austin did not mention it.

Haniyeh left the Gaza Strip in 2019 and had lived in exile in Qatar. Israel has targeted Hamas figures in Lebanon and Syria during the war, but going after Haniyeh in Iran was vastly more sensitive. Israel has operated there in the past: It is suspected of running a yearslong assassination campaign against Iranian nuclear scientists. In 2020, a top Iranian military nuclear scientist, Mohsen Fakhrizadeh, was killed by a remote-controlled machine gun while traveling in a car outside Tehran.

During Haniyeh’s last hours in Iran, a close ally of Hamas, he was smiling and clapping at the inauguration ceremony of the new President Masoud Pezeshkian. Associated Press photos showed him seated alongside leaders from the Palestinian Islamic Jihad militant group and Hezbollah, and Iranian media showed him and Pezeshkian hugging. Haniyeh had met earlier with Khamenei.

Hours later, the strike hit a residence Haniyeh uses in Tehran, killing him, Hamas said. One of his bodyguards was killed, Iranian officials said. Hamas official al-Hayya later said on Iranian state television that Haniyeh was killed by a missile.

Iran’s powerful Revolutionary Guard warned Israel will face a “harsh and painful response” from Iran and its allies around the region. An influential Iranian parliamentary committee on national security and foreign policy was to hold an emergency meeting on the strike later Wednesday.

Hamas’ military wing said in a statement that Haniyeh’s assassination “takes the battle to new dimensions and will have major repercussions on the entire region.”

Netanyahu has said Israel will continue its devastating campaign in Gaza until Hamas is eliminated. On Wednesday, he asserted that “everything” Israel has achieved in recent months was because it resisted pressure at home and abroad to end the war.

Israel’s bombardment and offensives in Gaza have killed more than 39,300 Palestinians and wounded more than 90,900, according to the Gaza Health Ministry, whose count does not differentiate between civilians and combatants.

After months of pounding, Hamas has shown its fighters can still operate in Gaza and fire volleys of rockets into Israel. But it is unclear if it has the capacity to step up attacks in retaliation over Haniyeh’s killing.

Besides a direct retaliation on Israel, Iran could work to increase attacks through its allies, a coalition of Iranian-backed groups known as the “Axis of Resistance,” including Hezbollah, Hamas, mainly Shiite militias in Iraq and Syria and the Houthi rebels who control much of Yemen.

As a show of support for Hamas, Hezbollah has been exchanging fire almost daily with Israel across the Israeli-Lebanese border in a simmering but deadly conflict that has repeatedly threatened to escalate into all-out war.