A rift over potential tolls in the Strait of Hormuz opened between Washington and Tehran on Saturday, throwing a week-old ceasefire into uncertainty just as negotiators prepared for a first round of talks in Switzerland. President Donald Trump declared on his Truth Social platform that no fees would be levied on vessels transiting the waterway during the 60-day truce or beyond, “unless they are imposed by and for the United States of America” should a final accord fail to materialise. The post, which framed any such charges as reimbursement for America’s role as the “Guardian Angel” of the Middle East, came hours after Iran’s military command announced it had closed the strait to commercial shipping, accusing the US and Israel of violating the ceasefire through strikes in southern Lebanon.

The state of maritime traffic became immediately contested. Iran’s armed forces general staff directed ships to avoid the area, citing security risks and describing the closure as a first response to disregarded commitments. By contrast, the United States Central Command (CENTCOM) reported that 55 merchant vessels carrying an estimated 17 million barrels of oil had crossed the strait during the day and that navigation remained active under American monitoring. CENTCOM assessed the threat level as moderate, while warning of naval mines and ongoing clearance operations. Viewed from Washington, maintaining the free flow of shipping was essential to denying Tehran coercive leverage over a chokepoint through which a significant share of global oil exports passes.

The toll dispute strikes at a core ambiguity in the 18 June memorandum of understanding between the two adversaries. Although the text guarantees free passage during the 60-day negotiating window, it left unresolved whether Iran might later introduce a “service fee”—a possibility Tehran had raised in the days before the truce. Trump’s statement was interpreted in European and Latin American diplomatic circles as an attempt to pre-empt any Iranian claim to a right to tax shipping and to assert that Washington, not Tehran, would determine the strait’s post-ceasefire regime. His characterisation of a US-imposed levy as compensation for past and present protection underscored a persistent demand that partners bear a greater share of regional security costs.

The diplomatic path forward remains fragile. A US delegation including Vice-President JD Vance, Special Envoy Steve Witkoff, and Jared Kushner is due to meet Iranian Foreign Minister Abbas Araghchi in Switzerland on Sunday, but Araghchi signalled that Tehran would not proceed unless the memorandum’s provisions—particularly the cessation of hostilities on all fronts, including Lebanon—were honoured. With Israeli operations in southern Lebanon continuing, the first formal contact since the signing risks stalling even as the 60-day clock ticks. Pakistan, which has acted as an intermediary, now confronts the immediate task of persuading both capitals to separate unresolved military grievances from the diplomatic calendar.