How might Iran respond to Israel's strikes on Tehran and Beirut?

Iran has been dealt a heavy blow to its regional reputation and sovereignty by the attack which killed Hamas political leader Ismail Haniyeh and his bodyguard early on Wednesday morning.

Details surrounding the nature of the aerial strike on a Tehran apartment have yet to be disclosed, but it has been widely attributed to Israel.

The Haniyeh killing is both a structural and psychological blow for Iran. The scale and audacity of the attack on Iran’s capital city – likely conducted by Israel’s notorious spy agency Mossad - will have left Iran with little choice but to respond.

It will have to reassert its strength and authority in the region, but to what extent and on what level remains to be seen.

What might Iran be mulling?

The intelligence breach and apparent display of Israel’s operational capacities within Iranian borders will be regarded as an embarrassment by Tehran.

There will be serious questions swirling around Iran’s political and military establishment over how the attack was able to happen, although it is not the first time Israel has conducted assassinations on Iranian territory.

While the attacks hit Lebanon and Iran’s capitals, they threaten the stability of the region and have awoken its deep alliances which unite in opposition to Israel.

Iran’s formidable Islamic Revolutionary Guard Corps (IRGC) which holds sway in state affairs said that Israel would be met with a “harsh and painful response” in the wake of the Palestinian leader’s killing.

“Iran and the resistance front will respond to this crime,” it said, referring to Iran’s so-called Axis of Resistance proxies across the Middle East.

Some analysts have suggested that Iran will be eager to rebuild its reputation domestically by publicly mobilising its forces at home and regionally through its allies, like the Houthis in Yemen or the Islamic Resistance groups in Iraq.

As head of Hezbollah’s highest military body, the Jihad Council, Fuad Shukr, who was killed by Israel in the Beirut strike, was believed to be particularly close to the IRGC which plays a key role in training, arming and funding the Lebanese Shia group.

A response could see the mobilisation of the paramilitary groups under Iran’s backing known as the Axis of Resistance; the Syrian regime, Hezbollah, the Yemeni Houthi group, the Islamic Resistance groups in Iraq and Hamas in Gaza.

All the paramilitary groups have condemned Haniyeh’s killing – who was regarded across the region as a face of resistance to Israel and the US.

Since October, the groups have been attacking Israeli assets, or US military assets, in support of Hamas’s fight against Israeli forces in Gaza.

The Houthis announced a three-day period of mourning following Haniyeh’s death.

The Iraqi Popular Mobilization Forces, which falls under the Islamic Resistance groups, said that the assassination of Haniyeh "will strengthen the resolve of the resistance fighters to continue on their path."

Its base was hit by a US air strike overnight on Tuesday, shortly after the Islamic Resistance threatened to respond to the Israeli strike on Beirut.

During the Gaza war, the Islamist groups have waged attacks within the ‘rules of engagement’ – conducting strikes on military infrastructure rather than civilian.

But the direct attack on Tehran and Beirut will have crossed these invisible lines, creating leeway for Iran to launch a greater aggression.

Dilemma for Iran: to contain or escalate?

The hostility between Israel and Iran is as much a war of words as it is actions, and threats of revenge have poured in after the attacks.

European diplomats will likely be gently pushing Tehran towards a ‘measured’ response of containment, while there will be regime hardliners who will be advocating for a grave escalation on Israel - which could drag in the US.

Throughout the Gaza conflict, Iran said it does not desire a major confrontation with Israel and at times has distanced itself from the aggressive rhetoric of some of its proxies.

It has a precedent of both responding in kind to Israeli assaults or choosing not to respond at all.

When a senior IRCG commander was killed by an airstrike widely attributed to Israel on its consulate in Damascus in April, Tehran launched a barrage of hundreds of drones and missiles over Israel’s airspace, marking the first direct assault between the two historic foes that again threatened to ignite the wider region into war.

But when top IRCG commander Qassem Soleimani was killed by a US-ordered air strike in 2021 and when nuclear scientist Mohsen Fakhrizadeh was reportedly assassinated by Israeli agents in 2020, the Islamic Republic did not strike back.

Where could be targeted?

Other possibilities lie with a direct assault by Hezbollah, who are geographically closest to Israel and have been waging hundreds of attacks on Israeli military bases and infrastructure since 8 October.

The group recently unveiled new weapons in the form of surface-to-air missiles which it said successfully deterred Israeli jets in Lebanon’s airspace.

It also showcased its ability to infiltrate airspace undetected by the publication of a series of drone footage taken miles into Israeli territory showing Haifa port and air defence facilities, planes and fuel storage units and published identification details of Israeli military officers.

The footage spooked Israel which is dependent on its air defence missile system to deter hostile aerial invasions.

US military bases in the region, including in Iraq or Kuwait, could be circled by Iran. Kataib Hezbollah, the Iraqi branch of Hezbollah brigades, has long demanded that all US forces leave western Iraq.

The militant group has come under previous US strikes which are rarely publicly acknowledged by Washington.

Another Iraqi group known as the Popular Mobilization Forces (PMF) said several of its members were killed by the US strike on Tuesday and has vowed to retaliate.

It is also claiming Kuwait’s involvement, blaming the Gulf nation for being a base from which the US can launch attacks, according to Al Jazeera.

Challenge for new Iranian president

The assassination of Haniyeh on Iranian soil is a challenge for new Iranian president Masoud Pezeshkian.

He will be keen to assert his influence and possibly attempt to seek international avenues to condemn Israel through the United Nations.

Iran’s mission to the United Nations stated that the response would be “harder and intended to instil deep regret” in the perpetrator in a post on X on Wednesday.

At Pezeshkian’s inaugural ceremony on Tuesday only hours before Haniyeh was killed, he said that “Improving and strengthening relations with neighbours” would be a key policy of his administration.

But he also issued a veiled threat to Western nations, stating that “those countries” which provide “the Zionist regime” with weapons to kill children in Gaza “cannot breach humanity to others”.

Certainly, over the coming days, as mourning continues for Haniyeh and Shukr, Iran will be calculating whether to pursue Pezeshkian's policy of strengthening neighbourly relations - perhaps by uniting behind its common enemy, Israel.