Hamas' political chief Ismail Haniyeh was killed by a "short-range projectile" launched from outside of his accommodation in Tehran, Iran's Revolutionary Guards said.
"This terrorist operation was carried out by firing a short-range projectile with a warhead of about 7 kilograms — causing a strong explosion — from outside the accommodation area," the Guards said in a statement.
The Guards again blamed Israel for Haniyeh's killing, adding that it was "supported by the United States."
The statement said that Haniyeh's death would be avenged and that Israel would receive "a severe punishment at the appropriate time, place and manner."
Israel has not claimed responsibility for Haniyeh's killing, which happened Wednesday in the Iranian capital, after he attended the swearing-in of Iran's new president, Masoud Pezeshkian.
His death sparked fears that Israel's military campaign against Hamas in Gaza and the conflict with Hezbollah in Lebanon could turn into a larger regional conflict with Iran.