A Truce of Competing Blockades: The April US–Iran Ceasefire and the Contest for the Strait of Hormuz

Key Judgements

• The 7–8 April US–Iran ceasefire is likely the most consequential diplomatic arrangement of the 2026 Iran war, as the first bilateral US–Iran accord since 1981 and the first of the conflict to tie military de-escalation directly to a physical chokepoint; however, the 8 June downing of a US Apache helicopter over the strait, which Washington attributes to Iran, has probably brought the framework to its weakest point yet.
• The framework’s central structural flaw is that it suspended strategic strikes while leaving both sides’ coercive instruments intact; because Iran’s closure regime and the US naval blockade each meet the other party’s definition of a ceasefire violation, leverage enforcement and truce violation have become almost certainly indistinguishable, driving the recurring escalation cycles of May and early June.
• If the proposed memorandum of understanding is not signed within the next two to three weeks, the ceasefire will probably continue degrading through calibrated attrition rather than collapsing outright; however, a US military response to the helicopter downing, or further autonomous Israeli action, raises a realistic prospect that Iran executes its 1 June threat to fully close the strait and activate the Bab al-Mandeb, globalising the energy shock.

Objective

This report assesses why the April 2026 US–Iran ceasefire represents a structural departure from previous arrangements between the two countries, examines the dynamics driving its erosion through May and early June, and evaluates the implications of a full collapse for regional escalation and global maritime security.

Context

The 2026 Iran war began on 28 February with coordinated US–Israeli strikes that killed Supreme Leader Ali Khamenei; Iran retaliated by closing the Strait of Hormuz, through which approximately one fifth of global seaborne oil transited before the conflict. On 7–8 April, following Pakistani mediation, Washington and Tehran agreed a conditional two-week ceasefire, conditioned by President Trump on the “complete, immediate, and safe opening” of the strait. The 11 April Islamabad talks ended after 21 hours without agreement, and the ceasefire was extended indefinitely. On 13 April the United States imposed a naval blockade on Iranian ports; Iran briefly reopened the strait on 17 April before closing it again. Through May, Tehran formalised a permit-and-toll regime under the newly created Persian Gulf Strait Authority, while negotiators converged on a one-page memorandum of understanding, reported on 28 May, extending the ceasefire, prohibiting tolls, and requiring Iranian demining within 30 days. Trump declined to endorse the draft, and a late-May cycle of US strikes on Iranian launch sites, Iranian missile fire toward a US base in Kuwait, and drone exchanges preceded Iran’s 1 June suspension of indirect messaging and its threat to “completely” block the strait, sending oil prices up more than 7 percent. On 7–8 June, Iran and Israel exchanged direct missile and drone fire for the first time since the truce began, and on 8 June a US Army Apache helicopter was downed near the strait, prompting Trump to state on 9 June that the United States “must, of necessity, respond” while claiming a comprehensive deal could be signed within days.

Analysis

Why the April framework stands apart. Previous arrangements between the parties were either multilateral, externally guaranteed, or narrowly military in scope. The June 2025 ceasefire ending the Twelve-Day War, mediated by the United States and Qatar, froze hostilities without resolving the underlying nuclear and missile disputes, and lapsed on 28 February 2026, the day the current war began. The April framework differs in three respects. It is the first bilateral accord agreed between Washington and Tehran since the 1981 Algiers Accords, reached through a novel Pakistani channel. It fuses military de-escalation with economic restoration by making the truce conditional on the physical reopening of the Strait of Hormuz, a linkage no previous US–Iran understanding has attempted. It is also phased, with the draft memorandum converting the truce into a 30-day negotiating track covering navigation, sanctions relief, and Iran’s nuclear programme. The framework is therefore probably the most significant diplomatic opening between the two states in four decades; its failure would discredit the only functioning channel for ending the war.

A ceasefire of competing blockades. The framework’s design flaw is that it suspended strategic strikes while leaving both parties’ coercive instruments in place. Iran retains physical control through mines, IRGC vetting of transits, and a toll regime under which vessels have reportedly paid up to USD 2 million per passage; the United States retains a naval blockade of Iranian ports it claims costs Tehran USD 500 million daily. Each instrument meets the other side’s definition of a ceasefire violation: Tehran characterises the blockade and associated tanker seizures as “maritime robberies” breaching the truce, while Washington treats Iranian drone launches and the toll regime as aggression requiring “self-defence” strikes. Routine leverage enforcement is therefore structurally indistinguishable from violation, as the late-May escalation cycle demonstrated. A second flaw compounds the first: the framework is a bilateral answer to a triangular war. Israel is only loosely bound by the arrangement, and its continued operations in Lebanon, cited by Tehran as the trigger for its 7 June missile launches, together with retaliatory Israeli strikes reportedly conducted against US wishes, mean the truce’s survival depends on an actor it does not formally constrain.

The limits of Iranian leverage. Iran’s chokepoint strategy is potent: Hormuz traffic has fallen roughly 90 percent since the war began, with only around 150 transits since 1 March, and the new Persian Gulf Strait Authority has converted ad hoc disruption into an institutionalised permit system JPMorgan estimates could yield USD 70–90 billion annually. The capability nonetheless carries significant limits. Iran’s own exports depend on Chinese buyers, yet Beijing has publicly aligned with Washington against any toll regime, constraining the strategy’s principal customer base. US Treasury designation of the Authority exposes toll-paying shippers to secondary sanctions, undermining revenue extraction. Iran’s late-May activation of an offshore loading node on its Gulf of Oman coast, outside the strait, indicates Tehran is hedging against its own closure. Months of US air operations have attrited launch sites, naval craft, and mining assets, while Iran’s claim of USD 270 billion in war damages and demand for reparations probably reflect acute economic strain rather than negotiating confidence. The 17 April precedent, when Iran briefly reopened the strait, further suggests closure functions as a bargaining instrument rather than an end state. US leverage faces parallel constraints: the Project Freedom escort operation was suspended within roughly 72 hours after Iranian fire on US destroyers, Lloyd’s List has recorded 26 blockade evasions, and the Apache downing shows enforcement carries rising costs.

The Tanker War precedent. The closest historical analogue is the 1984–88 Tanker War phase of the Iran–Iraq conflict, which clarifies how the adaptation balance has shifted. In the 1980s, Iranian attacks on Gulf shipping prompted the reflagging of Kuwaiti tankers and the US Navy’s Operation Earnest Will convoy system, the direct ancestor of Project Freedom; when the USS Samuel B. Roberts struck an Iranian mine in April 1988, the United States responded with Operation Praying Mantis, destroying much of Iran’s surface navy in a single day. Critically, the Tanker War never closed the strait: only a small fraction of transits were attacked, and convoying and deterrence adapted faster than Iranian raiding. In 2026 that adaptation cycle has likely inverted. Iran has shifted from hit-and-run raiding to administrative control, layering permits, tolls, mines, and shore-based drones into a system that has collapsed traffic to a degree the 1980s campaign never approached. Its force structure has also become more survivable: where Iran’s 1988 fleet was concentrated and rapidly attrited, the current architecture of small craft, dispersed shore-based missiles, and inexpensive one-way attack drones mirrors lessons from the Ukrainian battlefield and probably explains why three months of US air operations have not restored navigation. The precedent indicates a decisive Praying Mantis-style engagement is unlikely to be available against a distributed system; restoring transit will probably require negotiated demining or sustained attrition carrying significant escalation risk.

Alternative scenarios. Three trajectories are plausible over the next 30 days. First, phased restoration: the memorandum is signed, converting the ceasefire into a sequenced track of mutual relief, Iranian demining and toll suspension proceeding in parallel with blockade easing. This outcome aligns with both sides’ mounting economic costs and Trump’s 8 June claim that a deal could be signed within days, but remains hostage to spoiler incidents and to Israeli operations the framework does not bind. Second, calibrated attrition, probably the most likely near-term path: no signature emerges, the ceasefire survives in name, and enforcement-violation cycles continue, each incident hardening official language, entrenching the toll regime, and sustaining an elevated oil risk premium without tipping into full war. Third, full rupture: a US retaliatory strike for the Apache downing, or a further direct Israel–Iran exchange, triggers execution of Tehran’s 1 June threat to completely close Hormuz and activate the Bab al-Mandeb through the Houthis, whose 8 June missile launch at Israel suggests the announced “security belt” between the two straits is likely more than rhetorical. This scenario would almost certainly terminate the diplomatic track, produce a dual chokepoint crisis across Gulf and Red Sea routing, and risk renewed strategic strikes on Iran. The decisive variable is probably whether Washington’s response to the helicopter downing is calibrated to preserve the negotiating track or sized to restore deterrence at its expense.