Iran's Revolutionary Guards said on Saturday that Hamas leader Ismail Haniyeh was slain in Tehran by a short-range projectile with a warhead of about 7 kg, and vowed severe revenge.
Wednesday's assassination has drawn fears of direct conflict between Tehran and its arch-enemy Israel in a region shaken by Israel's war in Gaza and a worsening conflict in Lebanon.
Revenge for the killing of the Hamas leader will be "severe and at an appropriate time, place, and manner," the Guards' statement added, blaming the "terrorist Zionist regime" of Israel for his death.
Iran and Hamas have accused Israel of carrying out the strike that killed Haniyeh hours after he attended the inauguration of Iran's new president.
Israeli officials have not claimed responsibility.
According to Reuters, the statement by the Guards force also accused the "criminal US government" of supporting the attack which Iranian media said was in a northern suburb of Tehran.
Haniyeh was buried on Friday in Qatar, where he was based.
