Iranian Supreme Leader Ali Khamenei said on Wednesday that Tehran views it as a duty to avenge the killing of Hamas leader Ismail Haniyeh in the capital hours earlier.

"The criminal and terrorist Zionist regime martyred our beloved guest inside our house and made us mournful, but it paved the way for a harsh punishment to be imposed on it," he said in a statement quoted by the state-run IRNA news agency.

The newly inaugurated Iranian President Masoud Pezeshkian also threatened Israel after the attack, saying that "we will defend our land and make them regret their actions."

Iran's Islamic Revolutionary Guard Corps (IRGC) said in a statement that the assassination "will be met with a harsh and painful response," adding that "Iran and the resistance front will respond to this crime."

The Israeli government has not commented on Haniyeh's death.

Iranian Foreign Ministry spokesman Nasser Kanaani said on Wednesday that the blood of Haniyeh "will never be wasted," according to Reuters.

"Haniyeh's martyrdom in Tehran will strengthen the deep and unbreakable bond between Tehran, Palestine, and the resistance," said Kanaani.

Haniyeh was killed "in a Zionist airstrike on his residence in Tehran" after attending the inauguration of Pezeshkian, said Hamas according to the Associated Press.

Based in the Qatari capital of Doha, Haniyeh was one of the most senior members of Hamas, along with the terror group's leader in Gaza Yahya Sinwar.

Khamenei hosted Haniyeh and Palestinian Islamic Jihad leader Ziyad al-Nakhaleh in Tehran earlier this week.

Haniyeh's death came a few hours after the assassination by Israel of senior Hezbollah official Fuad Shukar in the heart of Beirut, which was acknowledged by the Israeli military.

Pezeshkian warned on Monday that a potential Israeli attack on Lebanon "could backfire and have severe consequences for the Zionists themselves," according to the semi-official Mehr News Agency.

The Israeli strike in Beirut came days after Iran's Lebanese terror proxy killed 12 children and wounded over 40 others in a rocket attack on Israel's Golan Heights that fell next to a soccer pitch in the Druze town of Majdal Shams.