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President Joe Biden has promised to retaliate after a drone attack claimed by Iranian-linked militias killed three US soldiers in Jordan but his response could lead to war with Iran if he does not tread carefully, analysts have warned.
After previous attacks on its troops, the US has responded by striking Iran-linked targets in Iraq and Syria with the aim of deterring further violence. A large strike on similar targets is now considered likely after Mr Biden vowed to “hold all those responsible to account at a time and in a manner of our choosing”.
But some in US Congress are calling for a more extreme response, such as strikes against military targets within Iran.
Such a move could lead to a wider regional war that the US does not want, analysts warned.
“A hit on the Islamic Revolutionary Guards Corps [IRGC] inside Iran would invite another strike on US troops, producing a cycle” said Mark Pyrus, a security and defence analyst focused on Iran.
"Where then do we go? The targeting has the potential for being pivotal."
Washington has faced similar dilemmas, including repeated decisions of how to respond to attacks on US troops by the Iran-backed Kataib Hezbollah militia in Iraq while maintaining relations with the Iraqi government and avoiding war with Iran.
Against a backdrop of regional tension inflamed by the Israel-Gaza war, Mr Biden faces a difficult balancing act.
Here are some of his options for retaliation, based on previous US military action.
A large strike against Iran-backed militia bases in Iraq and Syria is likely and would be in line with previous US retaliations.
The US has repeatedly carried out similar strikes since militias resumed attacks on US forces in both those countries in 2017.
The biggest target is the militia stronghold of Jurf Al Sakhar in Iraq. The US has repeatedly bombed the town, most recently hitting Kataib Hezbollah “headquarters, storage and training locations for rocket, missile and one-way attack UAV capabilities” on January 23.
The town, which was emptied of residents in 2014 by Kataib Hezbollah in a move condemned by human rights groups, has been taken over by the group and allied militias. It was one of the first targets authorised by Mr Biden in 2021.
Surrounded by palm groves and ringed by checkpoints patrolled by militias, the no-go zone for the official Iraqi army includes training sites for the Popular Mobilisation Forces (PMF) and, allegedly, foreign fighters.
More importantly, it houses research, development and construction sites for Kataib Hezbollah’s missile and drone programmes.
But the Americans would face problems with this option: because of the sporadic nature of the US-militia clashes, Kataib Hezbollah will have had time to disguise targets, build shelters and take other protective measures.
Air strikes there in the past have not had lasting damage. For example, after an Iran-backed militia attack in March 2020 that killed two US soldiers and one British medic at Al Asad airbase in Iraq, the US struck back at the site.
The US military said “the destruction of these sites will degrade Kataib Hezbollah’s ability to conduct future strikes". Yet despite exchanges of militia rocket fire and American air strikes in recent years, the group’s capabilities have grown to short-range ballistic missiles – far deadlier than their previous rocket arsenal – and an array of Iran-designed drones.
The US could also hit other bases, including in Syria, where previous strikes have destroyed weapons and limited the capability of Iranian proxies.
But militias are engaged in smuggling weapons and can replenish their stocks, which is one reason why some analysts argue only much larger US air strikes – perhaps dropping scores or even hundreds of bombs – will deter attacks.
F-15s, which can carry up to 10,000kg of bombs, have been used in previous US strikes on Jurf Al Sakhar and will probably be used again.
The jets carry a far higher load than the MQ-9 Reaper drone, which is commonly used against lightly armed militias by the US but carries about 1,700kg of bombs – one was recently shot down in eastern Iraq.
The jets fly well above portable militia missile defences and are equipped with “targeting pods” such as the Dragon’s Eye, which can track moving ground targets and people but cannot “loiter” for hours like drones.
A strike aimed at killing one or several militia commanders with the aim of disrupting militia command structures and deterring them from launching further attacks would be considered an escalation.
The US could strike militia commanders linked to the IRGC, or even Iranian advisers themselves within Iraq, said Mr Pyrus.
Previous hits on militia commanders have led to escalation.
The US killed the Kataib Hezbollah founder, Abu Mahdi Al Muhandis, alongside Iranian Maj Gen Qassem Suleimani in a drone strike in 2020 near Baghdad airport.
While Sulaimani’s death provoked a furious Iranian response – the IRGC fired 12 ballistic missiles at US troops in Iraq that caused traumatic brain injuries to 109 soldiers – the death of Al Muhandis also prompted retaliation from militias within Iraq, leading to more rocket attacks and retaliatory US strikes.
A US drone strike in Baghdad this month killed a commander of the Harakat al Nujaba militia, Moshtaq Talib Al Saadi. Washington said he had “American blood on his hands”, suggesting he was targeted retribution, rather than due to his rank.
His militia has since repeated warnings that US attacks will not go unpunished.
The US may choose to hit mid-ranking officers within the militias in an attempt to avoid escalation, rather than militia commanders such as Akram Kaabi, who heads Harakat Hezbollah Al Nujaba, or Abu Fadak Al Mohammedawi, better known as Abu Fadak, who replaced Al Muhandis as head of Kataib Hezbollah.
Targets could include militia members involved in missile and drone programmes. The US has the capability to track enemies over long periods using Reaper drones that can circle targets for up to 27 hours.
It could also use larger planes, such as the US AC-130J aircraft – a Hercules propeller plane bristling with large calibre guns – to track and strike targets. This happened in November with a strike on Kataib Hezbollah militants as they returned from firing a ballistic missile.
However, despite the advanced military technology, such strikes can still kill innocent Iraqi civilians accidentally. Strikes on Iraqi territory could also further jeopardise fraying relations between the US and the Iraqi government, which has condemned previous strikes as a violation of its sovereignty.
A more provocative response than striking Iran-linked sites and militants in Iraq would be to attack Iranian ships.
There is precedent for this: on April 18, 1988, the US sank an Iranian frigate in the Arabian Sea after an American warship had struck an Iranian mine. The warship was protecting commercial vessels that were under attack from the Iranians during the Iran-Iraq war.
“The US took out most of the Revolutionary Guard's navy,” says Joel Wing, an analyst who tracks violence in Iraq.
But Iran at that time was exhausted after a bloody eight-year war with Saddam Hussein’s Iraq. That is not the case today and Tehran has the largest missile force in the Middle East.
“If the US is considering striking a ship, Iran would probably reciprocate,” Mr Pyrus said. Iran currently has two vessels in the Red Sea, close to coalition forces.
“A hit on IRGC-Quds Force inside Iran would invite another strike on US troops, producing a cycle," Mr Pyrus said.
"Where then do we go? How do we close the cycle with the upcoming strikes? Will that be a consideration?”