Ayatollah Khamenei made the remarks on Wednesday, hours after Haniyeh, who had traveled to Tehran to attend the swearing-in ceremony of Iran’s new president, was killed in a dawn attack in the capital.
“The criminal and terrorist Zionist regime martyred our dear guest in our homeland and left us bereaved, but it also set the ground for a harsh punishment for itself,” the Leader said.
Ayatollah Khamenei commended Haniyeh’s years-long sacrifices in his fight against the Israeli occupation and said he was ready for martyrdom and sacrificed his children and households on this path.
“He was not afraid of embracing martyrdom in the way of God and saving God's servants, but we consider it our duty to avenge his blood in this bitter and horrific incident that came to pass in the Islamic Republic's territory," the Leader asserted.
The Leader also extended his condolences to the Islamic Ummah, the resistance front, the proud nation of Palestine as well as Haniyeh’s family and one of his companions, who was martyred with him.
Haniyeh was in Tehran to attend the inauguration ceremony of new Iranian President Masoud Pezeshkian on Tuesday.
Iranian authorities announced that rigorous investigations have been launched into the targeted killing of Haniyeh in the capital and the results will subsequently be released.
The Islamic Republic has declared three days of national mourning for the loss of the Palestinian resistance leader.
Palestinian groups have already condemned his assassination in the strongest terms, vowing to make those behind the assassination pay the price of the heinous act.
Haniyeh, 62, was born in a refugee camp near Gaza City and joined Hamas in the late 1980s during the First Intifada or uprising.
As Hamas grew in power, Haniyeh rose through the ranks and was appointed part of a “collective leadership” in 2004 and reached the Hamas top job in 2017.
Three of his sons were killed in an Israeli airstrike on Gaza in April.