Iran’s joint military command, the Khatam al-Anbiya Central Headquarters, announced on Saturday that the Strait of Hormuz would be closed to all vessel traffic, accusing the United States of failing to uphold the first clause of the memorandum of understanding (MoU) signed on 18 June and condemning Israel’s continued attacks on southern Lebanon. The statement, broadcast by Iranian state television, described the closure as a “first step” and warned that further measures would follow if what it called “aggression” persisted. The declaration came hours after a fresh ceasefire between Israel and Hezbollah was declared and then immediately contested by both sides, with Israeli airstrikes killing at least 16 people in the Nabatieh area, according to Lebanon’s civil defence.

The Iranian military command said the move was a response to “the explicit violation of the first clause of the post-war memorandum of understanding by the United States” and “the Zionist regime's continuous and ongoing violations of the ceasefire in southern Lebanon”. Iran’s foreign ministry spokesperson Esmail Baghaei, speaking to state media, added that Tehran had dispatched a negotiating team to Switzerland, where follow-up talks are scheduled, but stressed that the delegation would “demand that the other side fulfil its commitments” and that the entire MoU would be jeopardised if those commitments were not met. From Washington, Vice President JD Vance told Fox News he had seen no evidence of a closure and that commercial traffic had in fact increased, while US Central Command reported that 55 merchant vessels transited the strait on Saturday, carrying over 17 million barrels of oil. Mediator Pakistan confirmed that technical-level discussions would begin on Sunday in Bürgenstock, with Qatari representatives also present.

The reclosure of the Strait of Hormuz reverses a central element of the US–Iran interim agreement, which had led to a gradual resumption of shipping after a near-total blockade since late February that disrupted roughly 20% of global oil and gas flows. The MoU’s first article called for the “immediate and permanent termination of military operations on all fronts, including in Lebanon”, and for the withdrawal of foreign forces. Israeli officials, who are not signatories to the MoU, said they would not withdraw from southern Lebanon and insisted the conflict with Hezbollah was separate from the war with Iran. On the ground, Israel’s military said it struck dozens of Hezbollah targets in response to more than 50 projectiles fired at its forces overnight, while Hezbollah accused Israel of violating the ceasefire with an infiltration attempt near Nabatieh. The Lebanese health ministry reported further casualties in strikes near Sidon.

Diplomatic efforts now centre on the scheduled Sunday meeting in Switzerland, where US envoys Steve Witkoff and Jared Kushner are already on the ground, according to American officials. Vance indicated he expects to travel there “in the next couple of days”. The situation remains volatile: Iran has linked the strait’s status directly to the cessation of hostilities in Lebanon, while Washington maintains that the safe passage of commercial vessels remains uninterrupted. With the MoU’s implementation in doubt and the Israeli–Hezbollah front still active, the talks face an immediate test of whether the interim framework can be preserved.