The US military on Tuesday, 14 July broadcast warnings over public maritime radio channels advising all neutral vessels to immediately depart Iranian ports or abandon transit if Iran was their next port of call, according to VHF radio recordings obtained from a crew member aboard a merchant vessel operating near the Strait of Hormuz. The development marks a sharp escalation in the US-Iran maritime standoff, with Washington moving from diplomatic pressure to active enforcement.

What the Radio Message Said

'All neutral vessels are advised to immediately depart Iranian ports and discontinue transit if Iran is your next port of call,' the broadcast stated. The message further warned that following the formal commencement of the blockade, the measures would apply to all vessels regardless of flag or cargo — a sweeping directive that puts third-country shipping squarely in the crosshairs.

Vessels transiting to or from an Iranian port, the recording indicated, may be subject to interdiction and seizure. Humanitarian cargo exemptions are available but must be requested directly through the US military. Ships failing to comply, the message warned, would face force.

The Blockade Takes Effect

The US-led Joint Maritime Information Centre announced on Monday that the US Central Command would begin enforcing a maritime blockade targeting all Iranian ports and Iran's entire coastal area from 20:00 UTC on Tuesday. The blockade's scope — covering the full Iranian coastline — is notably broad and has no publicly stated end date.

In a separate radio transmission, the US military acknowledged that Iran had declared the Strait of Hormuz closed, but stated that US forces were prepared to maintain freedom of navigation and safeguard lawful commerce. 'A southern route of the Strait remains open,' the message said.

Strait of Hormuz: Two Routes, New Tension

Under a pre-existing US-Iran Memorandum of Understanding (MoU), commercial vessels have historically used two routes through the Strait of Hormuz: a northern route under Iranian control and a southern route closer to Omani waters, where the US military provides navigation assistance. With Iran now reportedly declaring the northern route closed, the southern corridor has become the sole operational passage — a chokepoint the US says it will keep open.

This comes amid a broader military confrontation. The US Central Command said on its official X account that it completed a five-hour wave of strikes against Iran earlier on Tuesday, targeting military facilities in Bushehr, Chabahar, Jask, Konarak, Abu Musa, and Bandar Abbas.

Global Shipping at Risk

The Strait of Hormuz is one of the world's most critical energy transit chokepoints, through which roughly 20% of global oil supply passes. A sustained blockade — or even the credible threat of one — carries significant implications for global energy markets, insurance premiums on tankers, and the supply chains of oil-importing nations including India, China, and Japan. Indian state-run oil importers are among those with active cargo movements in the region.

How Iran responds to the blockade enforcement and whether third-party nations challenge the US interdiction authority under international maritime law will be closely watched in the hours ahead.