Iranian media reported that Haniyeh was in a building for war veterans in Tehran when he was killed in an air strike around 2 AM local time (midnight GMT).
Hamas released a statement on Wednesday saying Haniyeh was killed in an Israeli raid on his residence in Tehran.
Ismail Haniyeh, 62, was seen as the overall leader of Hamas.
Israel has not commented on the attack, but it had vowed to destroy Hamas following an October 7 attack on southern Israel that killed 1,200 people.
Israel has since launched a major military operation in Gaza, which has resulted in the deaths of at least 39,400 people, according to the Hamas-run health ministry.
Haniyeh was reportedly in Tehran to attend the inauguration of the new Iranian President Masoud Pezeshkian, who was sworn in on Tuesday.
Hamas political bureau member, Musa Abu Marzuk called the attack a “cowardly act” and said it “will not go unanswered.”
Another senior Hamas official, Sami Abu Zuhri, said the group would “continue on its path.”
Iran’s foreign ministry stated that Haniyeh’s “martyrdom” would “strengthen the bond between Tehran, Palestine, and the resistance,” according to state media.
The Russian and Turkish foreign ministries also condemned the attack.
Haniyeh’s death came shortly after Israel claimed to have killed Hezbollah’s top military commander, Fuad Shukr, in an air strike in Beirut.
Hezbollah has not confirmed Shukr’s death but acknowledged that he was in the targeted building.
Haniyeh was a key Hamas member since the late 1980s and was imprisoned by Israel for three years in 1989.
The Hamster leader was exiled in 1992 but returned and was appointed Palestinian prime minister in 2006.
He continued to lead Hamas in Gaza after a violent conflict with Fatah in 2007 and was elected head of Hamas’s political bureau in 2017.
In 2018, the US designated Ismail Haniyeh as a terrorist, and he had been living in Qatar in recent years.
KanyiDaily recalls that a senior official from Hamas had invited Billionaire Elon Musk to visit Gaza, urging him to witness the extent of destruction caused by the Israeli bombardments.
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