The Iranian armed forces announced on Saturday the closure of the Strait of Hormuz to maritime traffic, blaming the United States for a “clear violation” of the first clause of a memorandum of understanding (MOU) reached only days earlier. The Khatam al‑Anbiya Central Headquarters declared the move a direct response to Israeli military operations in southern Lebanon, which Tehran says breach the agreed cessation of hostilities on all fronts. Within hours, the US Central Command (Centcom) stated that 55 merchant vessels carrying more than 17 million barrels of oil had transited the strait during the day, and that American forces remain “present and vigilant” to uphold every aspect of the accord.

Tehran’s military command framed the closure as the first step in a calibrated escalation, warning that “further measures” would be taken if the “aggression” continues. The Iranian foreign ministry stressed that the MOU obliges Washington to enforce a ceasefire in Lebanon—a requirement it says is being ignored. Viewed from Washington, the announcement is interpreted as a pressure tactic ahead of technical negotiations scheduled to begin on Sunday in Switzerland, but US officials insist the 60‑day ceasefire framework remains in place. President Donald Trump, posting on Truth Social, stated that no tolls or fees would be levied on Hormuz passage during or after the truce period, unless imposed by the United States if a final agreement is not concluded, characterising any future levy as reimbursement for long‑standing “guardian angel” security services provided to Middle Eastern countries.

The renewed closure threat injects fresh uncertainty into global energy markets: the strait is a conduit for roughly one‑fifth of seaborne petroleum. The fragility is compounded by the Israel‑Hezbollah ceasefire, announced on Friday and already undermined by cross‑border strikes that left at least 27 dead in Lebanon, according to Lebanese sources. Israeli officials say the strikes are retaliatory, while its ambassador to Washington maintains Israel remains committed to a truce. Analysts in London note that neither Israel nor Hezbollah were signatories to the US‑Iran MOU, leaving the Lebanon component without direct enforcement, and the wider understanding at risk of unravelling.

Diplomatic channels remain open. An Iranian delegation led by Foreign Minister Abbas Araghchi and including central bank and oil sector officials has arrived in Switzerland; the US side, represented by Vice President JD Vance, envoy Steve Witkoff, and Jared Kushner, is expected to join sessions mediated by Pakistan and Qatar. The immediate agenda covers technical discussions on nuclear issues and sanctions relief. However, Tehran has signalled that progress hinges on visible compliance with the MOU’s requirement to end hostilities on all fronts, making the physical state of the Hormuz passage and the durability of the Lebanon ceasefire the first practical tests as talks get under way.