Hamas leader Ismail Haniyeh was killed in an attack on his residence.
He was in Iran for the inauguration of President Massoud Pezeshkian, but was killed.
Haniyeh was attacked along with an Iranian bodyguard during a visit to Tehran, it was reported on Wednesday, July 31.
The Islamist faction said Haniyeh was killed in a "treacherous Zionist raid in Tehran."
Israel prefers not to comment on the situation.
The White House said it had been informed of the killing of Hamas political leader Ismail Haniyeh in Iran, but declined to comment.
The Palestinian militant group Hamas has expressed mourning over the death of its leader.
Haniyeh was the political leader of the group and spent most of his time in Qatar.
He served as a negotiator during the conflict between Israel and Gaza.
Hamas officials told Al-Aqsa TV that Haniyeh's killing would not go unanswered.
