Israel hits two top targets and dials the tension up to max

In addition, much of the weaponry used by Hamas in its war against Israel, including missiles and drones, have been supplied by Iran.

The killing of Haniyeh, who was seen offering prayers of thanks with other Hamas officials in his Qatar base following the 7 October attacks, helps fulfil a pledge by Israeli Prime Minister Benjamin Netanyahu to kill all Hamas leaders.

Leaky defence

Israel's ability to penetrate Iran's air defences to kill Haniyeh also represents a major humiliation for Tehran, which has spent billions of dollars upgrading its systems, including with the purchase of Russia's supposedly advanced S-300 set-up.

The Israelis had already demonstrated their ability to penetrate the S-300 when they carried out a retaliatory attack against Iran in April, after the Iranians launched their assault on Israel.

Israeli warplanes bombed an air defence facility near Isfahan in central Iran, site of some of Iran's most sensitive nuclear installations, and destroyed an S-300 battery. 

For Israel to conduct an aerial strike right in the heart of the Iranian capital just after the country had sworn in a new president is deeply embarrassing for the regime, which will be keen to demonstrate that it can mount an effective response.

Vowing revenge

The Iranian leadership was quick to denounce Haniyeh's assassination and to vow to avenge his death. Supreme Leader Ali Khamenei warned of "severe punishment" for "the criminal and terrorist Zionist regime… We view it as our duty to avenge his martyrdom which happened within the territory of the Islamic Republic of Iran."

Pezeshkian said Israel would "regret this cowardly killing" as he pledged to strengthen the bond between Iran and Palestine. "Yesterday, I raised his victorious hand," he said of Haniyeh. "Today, I must take his body on my shoulders."

As normal, Israel declined to comment on the assassination, merely confirming that the Israeli military was conducting a "situation assessment".

Israel's defence minister Yoav Gallant, while acknowledging the seriousness of the situation, insisted that Israel did not want to provoke a wider war, "but we are preparing for all possibilities".

How to respond

Haniyeh's assassination is certainly a major challenge for Iran, as it considers how best to respond. A supporter of the Palestinian cause, Iran also considers itself a pre-eminent military power in the region.

Yet the ease with which Israel defended itself from Iranian attacks, and the ease with which it conducts its own, is a significant blow for the ayatollahs, who will now come under intense pressure internally to show they can confront Israel.

Both Hezbollah and Iran now find themselves in a very challenging position, the assassinations of Shukr and Haniyeh having once again shown their vulnerability to Israel's superior military firepower.

If they overstep the mark in their response, they could open the door to US military intervention in support of Israel.

Together with allies such as the UK, Washington helped to defend Israel in April from the Iranian drone and missile barrage, while earlier this week, the US conducted its first airstrike against Iran-backed militias for several months.

Given the overall situation, the potential for escalation—from simmering conflict to all-out war—is there for all to see.

If the deaths of Shukr and Haniyeh are to be met with a reciprocal response, the Israelis may lose sight of their horizon.