Beirut. Hamas' top leader Ismail Haniyeh was killed Wednesday in a predawn airstrike in Tehran, Iran and the militant group said, blaming Israel for the assassination that risks escalating into a regional war. Iran's supreme leader vowed revenge against Israel.

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

Israel had pledged to kill Haniyeh and other Hamas leaders over the group's Oct. 7 attack on southern Israel. The strike came shortly after Haniyeh attended Iran's presidential inauguration in Tehran, and hours after Israel targeted a top Hezbollah commander in Beirut.

The assassination, due to its timing and location, has the potential to push Iran and Israel into direct confrontation if Iran retaliates. The US and other nations are working to prevent a wider conflict.

Iran's 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."

Israel and Iran previously risked war when Israel hit Iran's embassy in Damascus in April. Iran retaliated, leading to an unprecedented exchange of strikes, but international efforts contained the conflict.

Haniyeh's killing could derail Hamas' negotiations for a Gaza cease-fire and inflame tensions between Israel and Hezbollah. International diplomats were working to contain tensions after a weekend rocket attack killed 12 people in the Israeli-controlled Golan Heights.

A White House spokesman said there was "no sign that an escalation is imminent" in the Middle East and that a Gaza cease-fire was still possible. The US could not confirm reports of the Tehran incident. Secretary of State Antony Blinken said the US was not aware of or involved in the killing.

The UN Security Council held an emergency meeting to discuss the strikes but issued no collective message. The council members expressed concerns about potential escalation and called for restraint and diplomacy.

Hamas' consultative body is expected to name a successor soon, likely after Haniyeh's funeral in Qatar.

US Defense Secretary Lloyd Austin expressed hopes for a diplomatic solution on the Israeli-Lebanon border, saying, "I don't think that war is inevitable."

Israel often refrains from commenting on Mossad's operations. Israeli Defense Minister Yoav Gallant said Israel is preparing for all possibilities, without mentioning the Haniyeh killing.

Haniyeh, living in exile in Qatar since 2019, was targeted in Iran, a sensitive operation. Israel has targeted Hamas figures in Lebanon and Syria during the war, but attacking Haniyeh in Iran is significant. Israel is suspected of a years-long assassination campaign against Iranian nuclear scientists, including the 2020 killing of Mohsen Fakhrizadeh.

During his last hours in Iran, Haniyeh attended the inauguration of President Masoud Pezeshkian and met with Khamenei. Hours later, the strike hit his Tehran residence, killing him and one of his bodyguards.

Iran's Revolutionary Guard warned of a "harsh and painful response" from Iran and its allies. An Iranian parliamentary committee on national security and foreign policy held an emergency meeting on the strike.

Hamas' military wing stated that Haniyeh's assassination "takes the battle to new dimensions" and will have significant regional repercussions.

Netanyahu has said Israel will continue its campaign in Gaza until Hamas is eliminated. Israeli bombardments have killed over 39,300 Palestinians and wounded more than 90,900.

Hamas still operates in Gaza and fires rockets into Israel, but its capacity to retaliate for Haniyeh's killing is unclear. Iran could increase attacks through its allies, including Hezbollah, Hamas, and Shiite militias in Iraq and Syria.

Hezbollah has been exchanging fire with Israel across the Israeli-Lebanese border, threatening to escalate into war.