Rapid Reaction to US-Israeli Joint Strikes on Iran

With the scale of US force build-up in the region and the noise of speculation in recent days, achieving true tactical surprise was always going to be difficult. If anything, initiating operations in daylight may have been the closest available option.

For weeks, the core question has been which option US President Trump would pick from the menu his military planners would have put in front of him. The spectrum ran from limited, tightly-scoped strikes designed to further degrade elements of Iran’s nuclear programme to a broader campaign aimed at regime-change. In the days leading up to today, US-signalling was notably inconsistent, mixing restraint with threat inflation. Days ago, Vice President JD Vance said that there was ‘no chance’ the US will get into prolonged Middle East war.

Today’s announcement of ‘major combat operations’ under operation Epic Fury delivered by Trump’s 8-minute statement finally offers more clarity on the end state desired by the US: ‘To the great proud people of Iran, I say tonight that the hour of your freedom is at hand. Stay sheltered. Don’t leave your home. It’s very dangerous outside. Bombs will be dropping everywhere. When we are finished, take over your government. It will be yours to take. This will be probably your only chance for generations.’ Later, he said that his main concern is ‘freedom’ for the Iranian people, and that the US is working to make Iran a place that’s ‘safe.’ Read plainly, that is not the language of a limited, discrete operation designed solely to degrade specific capabilities.

Trump has opted for a wider more comprehensive operation against multiple targets and locations than was predicated. A wide range of military sites and installations have been struck across Iran in the early hours of this operation. If Iran’s response produces American casualties, the Trump administration will face sharper scrutiny from Congress and a public that is wary of open-ended Middle East entanglements.

Israel’s threat perception and strategic intent were far less ambiguous. Since the 7 October Hamas attacks, Israeli officials and analysts have consistently framed Iran as the ‘head of the snake’ driving the multi-front campaign against Israel and have argued that the centre of gravity sits in Tehran.

Against that backdrop, the three rounds of indirect US-Iran talks, facilitated by Oman, were widely read in Israel as slow, circuitous and unlikely to bridge the core gaps on enrichment, verification, sanctions relief and missiles. Reuters reporting today also underscores that Israel’s operation had been planned in coordination with the US months in advance, reinforcing the sense that diplomacy was running alongside military preparation rather than displacing it. This was the dual track military-diplomatic approach under wider ‘maximum pressure’.

For Israel, the lead up to this operation was clear and consistently framed as an unmissable historic opportunity to dismantle the Iranian regime and decisively cut down Iran’s capacity to threaten Israel directly or through its armed proxies.

RUSI’s Middle East Security Research Assistant, Alaa Zoubi, describes the situation in Israel: ‘Even if the official Home Front Command guidelines had not changed, public consciousness had already changed in the past 48 hours. It seems from the outset there was an assessment the negotiations between the US and Iran would not yield a result that would remove the threat as Israel perceives it. It is possible Israel assessed from the beginning of the nuclear talks that they were nothing more than an intermediate stage on the way to a broader conflict. However, waiting for the US indicates a strategic understanding between the US and Israel about joint decision-making, operational readiness and intelligence-sharing.’

Regime Change?

This is still the opening phase, with more unknowns than knowns. It is worth being precise about what ‘regime change’ is and is not in this context. A near-term scenario involving US ground forces installing a new government in Tehran is not what appears to be on the table.

What does seem to be emerging, however, is an aspiration that sustained strikes and pressure will so weaken key pillars of the Islamic Republic – military-security networks, senior clerical authority and the executive and judicial machinery – that space opens for alternative governing arrangements to consolidate from within Iran. That is inherently speculative, and it amounts to a very large gamble.

The more plausible near-term risk is that degradation of the centre does not translate into orderly transition, but into a contested interim period marked by uncertainty and potential fragmentation inside and across Iran. In that kind of environment, actors across Iran would compete for authority, resources and territorial control, while external players try to shape outcomes from the margins. We are not there yet – but the logic implied by today’s rhetoric and strike posture is one that could make that pathway more likely if escalation continues.

The question now is whether Iran can impose meaningful costs on the US and Israel, or whether we see a ‘paper tiger’ outcome, especially in the shadow of last year’s Operation Midnight Hammer, which exposed gaps between Tehran’s escalatory signalling and its ability to translate this into sustained effect against US and Israeli targets.

But this time was always going to be different. According to an Iranian source I spoke to earlier this week, ‘For Iran, there’s no limited strike scenario. Iran views any strike as the beginning of an all-out regime change war. Meaning, Tehran will immediately respond disproportionately. We may, for the first time after the Iran-Iraq war, see Iran in an existential fight. By harming/hurting US and Israel, Iran would hope to restore its lost deterrence.”

Iran does retain options. It can absorb the opening blows, surge missiles and drones, lean on proxies and look for asymmetric disruption in the Gulf and Red Sea. But its anti-access/area-denial (A2/AD) toolkit is constrained against a capable, networked US-Israeli air and missile campaign.

The Escalation Path is Unclear as of Now, but Key Variables to Watch Include:

Over the longer term, a harder question is whether the US would judge it necessary to deploy force elements on the ground to conduct direct bomb damage assessment (BDA) of key nuclear facilities and secure sensitive materials, such as Iran’s nuclear stockpiles. We are a long way from that scenario, but it cannot be ruled out if decision-makers conclude that remote surveillance cannot provide sufficient confidence about what has been destroyed, what has been moved and what could be reconstituted. A factor determining its likelihood would be leadership decapitation of senior regime and IRGC figures.

First: The GCC Response and Risk of Regionalisation. Iran has targeted five GCC states: the UAE, Qatar, Bahrain, Kuwait and Saudi Arabia. Gulf neighbours that have spent recent weeks trying to avert war suddenly found themselves in the line of fire in Iran’s first retaliatory salvo. This risks hardening Gulf public and elite sentiment against Iran. Even where missiles are intercepted, the message is that Gulf territory and civilians are acceptable collateral in a confrontation they did not choose. If there are casualties or significant damage, Gulf states will come under pressure to align more openly with the US operation, whether through political backing, force-protection or expanded access, and to claim the right to self-defence.

Second: Houthi Activity in the Red Sea and Bab Al-Mandab. Maritime security and safe passage through key energy chokepoints is a core UK interest and it will matter immediately if this conflict widens. It is important to be clear-eyed about Houthi agency. While the group is aligned with Iran and benefits from Iranian support, it has repeatedly shown it can act with its own operational logic and political incentives.

We are still in the very early stages of both the US-Israeli operation and Iran’s retaliatory cycle. But if Iran’s direct capabilities are degraded, the Houthis may be among the actors best positioned to escalate by increasing disruption and harassment along global shipping lanes and the energy corridor – through renewed missile and drone launches, attempted interdictions, or the threat of mining and swarming tactics that raise risk premiums even when attacks are intercepted.

Third: Iraq and Iran-Linked PMU Activity. According to Tamer Badawi, RUSI’s Associate Fellow, ‘Iran-backed armed groups in Iraq, mainly Kata’ib Hezbollah and to a lesser extent Harakat al-Nujaba, have responded to Israeli and US attacks on Iran with assertive statements promising attacks on US bases, without defining the perimeters of such attacks. Such attacks would very likely include the Iraqi Kurdistan Region and energy infrastructure in the KRI. There are rough odds that the Iran-backed Iraqi groups would attempt to target US targets in the GCC, reminiscent to similar attacks conducted on Saudi Arabia and the UAE in 2021 and 2022. Such a likelihood is high given that such a war is widely perceived to be existential for the Islamic Republic, the patron and leader of the ‘Axis of Resistance’ which those groups are a member of.

‘Not all Iran-backed Iraqi groups are equally invested given that each calibrates its positions based on political calculations. Those groups who became part of the Coordination Framework or closely linked to it are not expressing attacking intents, so far. This includes Asa’ib Ahl al-Haq and Harakat Ansar Allah al-Awfiya. The only outlier is Kata’ib Sayyid al-Shuhada who has been continuing such threats through proxy groups prior to the start of the war. It is still unclear if members of the Coordination Framework would become involved in such a war. Some of those groups may be either thinking pragmatically and giving up on the Islamic Republic or rather assigning to themselves the role of maintain Iran’s enduring legacy in Iraq.’

All of this is necessarily an early assessment based on partial information and the picture will sharpen as strike effects, Iranian decision-making and regional responses become clearer over the coming hours and days. RUSI will continue to monitor developments closely and provide expert analysis on the evolving situation.

© RUSI, 2026.

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