Haniyeh has been assassinated in the Iranian capital Tehran.
Haniyeh “passed as a result of a treacherous Zionist raid,” the movement said in a statement on Wednesday.
“The Islamic Resistance Movement Hamas mourns the sons of our great Palestinian people, the Arab and Islamic nation, and all the free people of the world,” it said.
Mousa Abu Marzook, a member of Hamas’ political bureau denounced the assassination as a “cowardly action” that would not go unanswered.
Iran’s Islamic Revolution Guards Corps (IRGC) had announced the martyrdom, saying that the assassination targeting the Hamas leader’s residence in Tehran had also claimed the life of one of Haniyeh’s bodyguards.
The development came amid Hamas’ all-out efforts to defend Gaza against an ongoing genocidal war by the Israeli regime, and the movement’s participation in negotiations aimed at bringing about a truce to end the brutal military onslaught.