According to Hamas, Haniyeh was killed in a "treacherous Zionist raid" on his residence in Tehran after participating in the inauguration ceremony of the new Iranian president.
Iranian state television also confirmed the assassination, stating that an investigation is underway and findings will be announced later.
The assassination comes just hours after Haniyeh's last public appearance at the inauguration ceremony of the new Iranian president in Tehran.
Haniyeh was a prominent Palestinian political leader and a symbol of Hamas. He was also a key figure in the Gaza Strip and had played a significant role in Hamas's leadership for over 20 years.
Haniyeh's life was marked by struggles against Israeli occupation and oppression. He was born in 1963 in the Beach Refugee Camp in western Gaza City and lived there until 2019 before moving to Qatar to lead Hamas's political bureau.
He was arrested several times by the Israeli army and spent three years in an Israeli jail on charges of being a member of the Hamas security service.
Haniyeh's assassination is seen as a significant escalation of tensions between Israel and Hamas, and is likely to lead to further retaliation from the group.
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