Ceasefire, failed Islamabad Talks, then a US naval blockade of Iran

At 10:00 a.m. eastern time on 13 April 2026 a United States naval blockade of Iranian ports took effect, announced by President Trump on 12 April after the collapse of the Islamabad Talks (see the war’s opening in US-Israeli strikes on Iran kill Khamenei; war begins and the closure arc in Iran closes Strait of Hormuz; Gulf states enter the war); US Central Command said the blockade — covering all maritime traffic entering or exiting Iranian ports, of all flags, while not impeding vessels transiting the Strait of Hormuz to or from non-Iranian ports — was implemented “in accordance with the President’s proclamation,” with US Naval Forces Central Command issuing a shipping advisory on 16 April.¹² The blockade ended a brief diplomatic opening. On the evening of 7 April — less than two hours before his own 8:00 p.m. ultimatum, in which he had warned that “a whole civilization will die tonight” — President Trump announced on social media a two-week ceasefire effective 8 April, brokered by Pakistan and conditioned on Iran reopening the Strait of Hormuz; the Israeli Prime Minister’s Office said it supported the suspension while stating the ceasefire did not apply to the war with Hezbollah in Lebanon — a scope Pakistani Prime Minister Shehbaz Sharif contradicted on 8 April, saying the ceasefire “covers everywhere including Lebanon” — and the President called it “A big day for World Peace!”³⁴⁵ Talks convened in Islamabad on 11-12 April, hosted by Prime Minister Shehbaz Sharif, with Vice President JD Vance leading the US delegation alongside Steve Witkoff, Jared Kushner and National Security Adviser Andrew Baker, and Speaker of Parliament Mohammad Bagher Ghalibaf leading Iran’s, with Foreign Minister Abbas Araghchi and central-bank governor Abdolnaser Hemmati; after roughly 21 hours across three rounds the talks failed over the nuclear program, the status of the strait, and sanctions sequencing — Iran demanded comprehensive sanctions lifting and the release of approximately $6 billion in frozen assets (a senior Iranian source told Reuters the United States had agreed to release frozen assets held in Qatar and other foreign banks; a US official denied it). In a 12 April post on X, Araghchi wrote that “when just inches away from ‘Islamabad MoU’, we encountered maximalism, shifting goalposts, and blockade.”⁶⁷

1. A blockade is an act of war under the customary law of naval warfare: the San Remo Manual on International Law Applicable to Armed Conflicts at Sea (paragraphs 93-104) treats blockade as a method of warfare available to belligerents in international armed conflict, subject to declaration, notification, effectiveness and proportionality requirements.⁸ The administration’s characterisation of the measure and its domestic legal basis drew immediate legal commentary distinguishing the belligerent-blockade framework from sanctions-based interdiction; the proclamation’s text and number had not been published in the Federal Register at the blockade’s effective date.⁹

2. The ceasefire’s structure paired a short fixed window and a single-condition opening (Hormuz transit) against a maximalist end-state demand (zero enrichment) and Iran’s sequencing demand (sanctions relief first). The Islamabad channel — Pakistan as broker, with Iranian officials and the President describing a Chinese nudge toward acceptance by the new Supreme Leader, Mojtaba Khamenei — remained the standing negotiating venue after the talks failed: a second Islamabad round convened around 20 April, and on 21 April, at Pakistan’s request, President Trump extended the ceasefire, citing a “seriously fractured” Iranian government.³⁶¹⁰¹¹

3. Enforcement of the blockade falls to US Central Command and Fifth Fleet assets already engaged in the strait campaign. On 19 April the destroyer USS Spruance fired disabling rounds into the engine room of the Iranian-flagged container ship Touska after six hours of warnings as the vessel attempted to reach an Iranian port, after which Marines of the 31st Marine Expeditionary Unit boarded and seized it — the cordon’s central enforcement event of the first week; the 22 crew members were transferred to Pakistan in early May.¹² The President’s 1 May 2026 letter to Congress stated that “[t]he hostilities that began on February 28, 2026, have terminated” — a characterisation that, if accepted, stops the War Powers Resolution 60-day clock under 50 U.S.C. § 1544(b); war-powers analysts contested the characterisation as major combat operations wound down in early May while enforcement operations continued.¹³¹⁴