The religious leader of Iran Ali Khamenei on August 1 conducted funeral prayers over the body of Ismail Haniyeh, political chief of Hamas, who was assassinated in Tehran the previous day, local media reported. 

Khamenei had vowed vengeance in a message on the day of the killing, blaming Israel for the attack following the hit against a senior ally on its territory. American reports noted that Haniyeh was killed by a blast from inside the apartment the Iranian state gave him. Secondary intelligence reports suggested that the Hamas leader was killed by a bomb which had been planted several months in advance of his stay. 

Khamenei said: “The criminal and terrorist Zionist regime [Israel] martyred our dear guest in our home and left us in mourning, but it also paved the way for severe punishment for itself.”

“In this bitter and difficult incident that occurred within the territory of the Islamic Republic, we consider it our duty to seek retribution for his blood.”

Khamenei has reportedly ordered retaliation by direct attack on Israel like the one carried out earlier in April in response to the bombing of Iran’s embassy compound in Damascus, Syria, that killed several top military commanders.

On April 13, Iran launched hundreds of missiles and drones at Israeli territories but caused only minor damage as most of the projectiles were intercepted.

Earlier, the secretary of Iran’s Supreme National Security Council, Ali Akbar Ahmadian, had said that "avenging Haniyeh's blood is Iran's duty." He added Haniyeh was the only influential person in the ceasefire talks, but Israel is not pursuing peace.

Iran’s ambassador to the United Nations also delivered a statement before the Security Council on July 31, stressing that “Iran reserves its inherent right to self-defence, by international law to respond decisively to this terrorist and criminal act when it deems necessary and appropriate.”

Tehran is also weighing up simultaneous attacks by its proxies in Yemen, Syria and Iraq, according to unofficial reports. The pressure to respond decisively is immense, particularly from the hardline Islamic Revolutionary Guard Corps (IRGC). They issued a swift and strongly worded statement promising a "harsh and painful response” against Benjamin Netenyahu’s government in Tel Aviv.

Earlier, Iran's ally, Russia's Kremlin spokesman Dmitry Peskov on July 31, condemned Israel's strike on Iran that killed Hamas political bureau chief Ismail Haniyeh, saying such actions undermine efforts to restore peace in the region.

"These actions are directed against attempts to restore peace in the region," Peskov told reporters during a regular press briefing in Moscow.

Following Iran's threat Israeli Prime Minister Benjamin Netanyahu said the Jewish state is at a high level of preparedness for any scenario, both defensively and offensively, after he completed a situation assessment with Israel's Home Front Command, his office said.

"We will exact a heavy price for any act of aggression against us from any arena," the Israeli prime minister said.