The dispute over the Strait of Hormuz has entered a more fragile phase, with the United States insisting the strategic waterway is open while Iran says shipping will remain restricted until Washington meets conditions linked to an interim agreement.

The divide comes as commercial traffic through the strait has fallen sharply. Six commodity vessels crossed on Tuesday, according to shipping data, down from nine the previous day and below a 10-day average of 11. Before the war, the waterway carried about a fifth of global crude oil and liquefied natural gas shipments.

US President Donald Trump said on 18 August that no talks with Iran were taking place or scheduled, while maintaining that Hormuz was “open and operating”. Iran has rejected that assessment and said the strait will remain closed until Washington fulfils the terms it says were agreed in June.

Iranian negotiator Mohammad Baqer Qalibaf said the conditions included lifting the US blockade on Iranian ports, removing oil sanctions, releasing frozen Iranian assets and ending military operations and threats. Tehran has presented those measures as prerequisites for reopening the waterway.

The disagreement is complicated by the fact that some vessels continue to move through Hormuz. Shipping data showed six commodity vessels crossing on Tuesday, even as most shipowners remained reluctant to use the route because of uncertainty over whether it is effectively open and under what conditions.

The United States has maintained a naval blockade of Iranian ports and said it has the capability to sustain the operation. Defence Secretary Pete Hegseth said on 13 August that Washington could maintain the naval presence indefinitely while increasing economic pressure on Tehran.

The June memorandum of understanding initially offered a framework for ending hostilities and reopening Hormuz. The White House said the agreement required Iran to make arrangements for the safe passage of commercial vessels and linked the reopening of the strait to broader commitments concerning Iran's nuclear programme.

That framework has since come under strain. Iran has accused Washington of failing to honour its commitments, while the Trump administration has rejected Tehran's interpretation of the agreement. Reuters reported on 17 August that negotiations for a permanent end to the war had stalled and that an Iranian official warned Tehran could adopt a “fully offensive” military posture if diplomacy failed.

A parallel effort involving Iran and Oman has offered a possible route towards easing the maritime dispute. Iran said it had reached an understanding with Oman over a transit route and was working on a joint statement, while Washington has opposed elements of the proposed arrangement, including possible Iranian-Omani management of parts of the passage and voluntary fees for vessels.

The dispute is also carrying an immediate economic cost. Brent crude reached $91.56 a barrel on 19 August, its highest level in three weeks, as traders continued to price in the risk of prolonged disruption. Major Chinese shipping companies have also kept tankers away from Hormuz since late July, adding pressure to an already disrupted energy market.

For now, the central disagreement remains unresolved: Washington says commercial navigation is available, while Tehran links a fuller reopening to the lifting of sanctions, the port blockade and military pressure. With shipping activity still well below normal levels and diplomacy stalled, the strait remains a key pressure point in the wider US-Iran confrontation.