Hamas’s armed wing said the death of Haniyeh, who was widely viewed as the group’s overall leader, would “take the battle to new dimensions” and have major repercussions.
The group attacked Israel on 7 October, killing around 1,200 people. Since the attack, Israel has vowed to destroy Hamas.
Haniyeh, who played an important role in negotiations over a ceasefire in Gaza, was killed hours after attending the inauguration of Iran’s new president, Masoud Pezeshkian, in Tehran.
A senior Hamas official told the BBC the killing took place in the same building where Haniyeh had stayed during previous visits to Iran.
Three Hamas leaders and a number of guards were with him in the same building, they said.
Khalil Al-Hayya, a senior Hamas official, told a news conference that a missile hit Haniyeh “directly”, citing witnesses who were with him.
The group’s leadership has been left in “a state of shock”, top Hamas officials have told the BBC.
Hours before Haniyeh was targeted, Israel said it had killed senior Hezbollah Fuad Shukr in Beirut.
Israel believes he was responsible for a rocket attack that killed 12 people in the Israeli-occupied Golan Heights on Saturday. Hezbollah has denied any involvement.
The Iran-backed group confirmed Shukr’s body was found among the rubble of the residential building which was struck. Four other people, including two children, were killed.
