BEIRUT :  Hamas leader Ismail Haniyeh was killed by an airstrike in Tehran, Iran, and the militant group said on Wednesday, blaming Israel for a shock assassination that risks escalating the regional conflict on multiple fronts.

There was no immediate comment from Israel, which has vowed to kill Haniyeh and other Hamas leaders over the group’s Oct. 7 attack on southern Israel. The strike came just after Haniyeh had attended the inauguration of Iran’s new president in Tehran, Iran said.

The killing could trigger retaliation against Israel from Iran or its powerful Lebanese ally Hezbollah and prompt Hamas to pull out of months of negotiations for a cease-fire in Gaza.

Hours earlier, Israel carried out a rare strike in the Lebanese capital Beirut that it said killed a top Hezbollah commander who was allegedly behind a weekend rocket attack that killed 12 young people in the Israeli-controlled Golan Heights. Hezbollah said Wednesday that it was still searching for the body of Fouad Shukur in the rubble of the building that was struck.

The U.S. and other nations had already been scrambling to prevent the Golan Heights strike from spiralling into an all-out war between Israel and Hezbollah when word came of the dramatic assassination of Hamas’ top political leader, Haniyeh, in Tehran.

There was no immediate reaction from the White House to the killing of Haniyeh. An Israeli military spokesman declined to comment. Israel often doesn’t comment on assassinations carried out by its Mossad intelligence agency or strikes on other countries.

It has repeatedly vowed to eliminate Hamas leaders wherever they are for the Oct. 7 attack, in which Hamas-led militants killed 1,200 people and took some 250 others hostage.

Hamas said Haniyeh was killed “in a Zionist airstrike on his residence in Tehran” after he attended the swearing-in of Iran’s President Masoud Pezeshkian on Tuesday, along with other Hamas officials and officials from Hezbollah and allied groups.

“Hamas declares to the great Palestinian people and the people of the Arab and Islamic nations, and all the free people of the world, brother leader Ismail Ismail Haniyeh a martyr,” Hamas said in its terse statement.

 In another statement, the group quoted Haniyeh as saying that the Palestinian cause has “costs” and “we are ready for these costs: martyrdom for the sake of Palestine, and for the sake of God Almighty, and for the sake of the dignity of this nation.”

Hamas officials did not immediately respond to requests for further comment.

In the West Bank, internationally backed Palestinian President Mahmoud Abbas condemned Haniyeh’s killing, calling it a “cowardly act and dangerous development.” Political factions in the occupied territory called for strikes in protest at the killing.

Haniyeh left the Gaza Strip in 2019 and had lived in exile in Qatar. The top Hamas leader in Gaza is Yehya Sinwar, who masterminded the Oct. 7 attack. In April, an Israeli airstrike in Gaza killed three of Haniyeh’s sons and four of his grandchildren.

 In an interview with the Al Jazeera satellite channel at the time, Haniyeh said the killings would not pressure Hamas into softening its positions amid ongoing cease-fire negotiations with Israel.

Meanwhile, Iraq’s Popular Mobilisation Forces, a coalition of Iranian-backed militias, said that a strike Tuesday night on a base southwest of Baghdad killed four members of the Kataib Hezbollah militia.

The group accused the United States of being behind the strike. Kataib Hezbollah, along with some of the other militias, has in recent months carried out attacks against bases housing U.S. troops in Iraq and Syria in retaliation for Washington’s support for Israel in the war in Gaza. U.S. officials did not immediately comment.

Israel is suspected of running a years-long assassination campaign targeting Iranian nuclear scientists and others associated with its atomic program. 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.

In Israel’s war against Hamas since the October attack, more than 39,360 Palestinians have been killed and more than 90,900 wounded, according to the Gaza Health Ministry, whose count does not differentiate between civilians and combatants.