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The US is reported to be greatly expanding the scope of its naval blockade of Iran, asserting the right to board and seize any ships it believes to be carrying “contraband” or “conditional contraband” bound for Iran from anywhere on the open seas. Respected maritime news and intelligence agency, Lloyd’s List, says this means that “almost any industrial cargo bound for Iran could plausibly be intercepted”. This will considerably raise the stakes in an already fraught situation.

Opinions are already divided as to how effective this “blockade of a blockade” is likely to be. The US president made the decision on April 12 to “seek and interdict every vessel in International Waters that has paid a toll to Iran. No one who pays an illegal toll will have safe passage on the high seas.” The intention was to make clear to Tehran that they were ultimately not in control of the strait and certainly wouldn’t be allowed to profit by imposing a charge on ships it allowed to pass through.

The problem for the US is that traffic through the strait remains largely at a standstill. Reuters’ live tracker of traffic in the strait suggests a considerable gathering of vessels on either side of the waterway, with very little evidence of ships actually transiting the strait.

It is, writes maritime strategy expert Basil Germond, of Lancaster University, a question of who can withstand more pain from the economic fallout. So the US plan to seek and seize ships wherever they are on suspicion of carrying almost any sort of industrial cargo is clearly aimed at increasing that pain for Iran.

Read more: US naval blockade of Strait of Hormuz: what it........

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