Iran Supreme Leader Ali Khamenei said Wednesday that avenging Hamas leader Ismail Haniyeh's assassination is "Tehran's duty" because it occurred in the Iranian capital.

Haniyeh, Hamas' chief political leader, was reportedly killed Tuesday in a missile strike while in Tehran to attend Iranian President Masoud Pezeshkian’s swearing-in ceremony. 

Israel is being blamed for the attack, after having previously promised to kill Haniyeh and other Hamas leaders after the October 7, 2023, attack on Israel in which 1,197 people were killing, resulting in Israel’s war in Gaza against Hamas. 

Khamenei also said said the attack provides the grounds for "harsh punishment" on Israel as a response, according to Reuters. 

“The criminal and terrorist Zionist regime martyred our dear guest in our house and made us bereaved,” he also reportedly also said in a statement.

Israel has yet to comment on the attack.

Iran has announced three days of public mourning across the country. A funeral ceremony will be held in Iran on Thursday. His body will then be transferred to Doha, Qatar, where he will be buried Friday, according to the Associated Press.