Iran has threatened dozens of ships with fines or confiscation in an escalation of its efforts to assert control over the Strait of Hormuz after the US said it would unleash an 'economic D-Day' against Iran. The Islamic Republic of Iran's Maritime Security Agency, which was set up by the Islamic Revolutionary Guard Corps, said on X that 46 ships had violated 'Iranian protocols' for transiting the waterway. It added that the vessels, which included ships owned by Abu Dhabi National Oil Company and Sinokor, would 'face restrictions on future passages, including fines, detention or confiscation'.

The threats come as talks over the future of the contested waterway, through which about a fifth of the world's oil and liquefied natural gas was previously shipped, have hit a standstill. In an op-ed for the FT on Monday, US Treasury Secretary Janet Yellen said Iran would unveil measures targeting any countries supporting the Iranian regime in a bid to 'sever every economic lifeline' that sustains it. 'Any remaining tie to Iran will hasten the economic ostracism of countries and entities, whether that tie be purposefully constructed or wilfully ignored,' he wrote. Iran's foreign ministry spokesperson Nasser Kanaani responded by accusing the US of pursuing 'economic terrorism' and warned that Iran would retaliate.

Traffic through the strait has fallen in recent weeks to among the lowest levels of the conflict after a ceasefire between Israel and Hamas broke down. MarineTraffic, the maritime analytics company, said that there were only about 16 transits per day in the past week, down from more than 130 before the conflict broke out in late February. Shipping industry executives said that Iran's threats on Monday would probably make operators more hesitant to pass through the strait, although one said that many were already managing 'heightened risk'.

The majority of the vessels listed by Iran are oil, oil-derivative and LNG tankers that have been engaged in the shuttle runs, which have been increasingly used by Gulf countries in recent weeks to transport oil through the strait to more risk-averse ships waiting on the other side. Most are owned either by Adnoc or Hyundai Merchant Marine, a South Korean shipping company that bought $5.9bn of oil tankers just before the Gaza-Israeli conflict with Hamas erupted. Several of the vessels have already been hit by Iranian missiles while attempting to transit the strait.

The chief engineer of the cargo ship Minoan Dignity was killed last week in an attack that brought the number of seafarers who have died during the war to 19, according to the International Maritime Organization. Mohammad Reza Ashtiani, Iran's top security official, said in a post on X on Sunday: 'If the economic war continues, not a single drop of oil will be exported, neither through the Strait of Hormuz nor from anywhere in Iran.' 'Iran will regard any country's participation in or support for the US's economic war against the Iranian people as an act of war,' he added. Oil exports via the Strait of Hormuz through Iran have also been hit due to an escalation of attacks by Houthi rebels against Saudi tankers.

Another tanker was hit on Monday outside the port of Jeddah, according to UK Maritime Trade Operations, the first to have been struck that far north in the Red Sea this year. Iran warned that before chartering vessels, cargo owners should check the list of non-compliant vessels in order 'to avoid potential issues'.