Analysts report that reduced crude oil supply and refiners' preference for producing diesel have contributed to a global shortage of heavy fuel oil for shipping. This scarcity, which occurs alongside existing constraints on key waterways, may drive up freight costs and impact broader global trade, though the precise extent of these economic effects remains under assessment.

Can Iran enforce a restricted zone in the Strait of Hormuz? Iran unveils plans for a restricted zone, but will Tehran be able to enforce it amid escalating tensions with the US? Iran says it plans to establish a new restricted zone around the Strait of Hormuz, a global energy chokepoint, after Tehran and Washington traded attacks on ships in the crucial waterway in what experts called a “dangerous escalation”.

The two sides have been engaged in on-and-off attacks since a 60-day memorandum of understanding (MoU), signed on June 17, expired last month. Recommended Storieslist of 3 items - list 1 of 3Multipolarity gives middle powers more choices, but fewer guarantees - list 2 of 3US, Iran engaged in tanker war: Where is the months-long conflict headed?

- list 3 of 3Iran touts military response as US maintains blockade, hits tankers The latest escalation started after Iran targeted US warships patrolling and escorting oil tankers trying to evade the Tehran-imposed blockade of the strait. Meanwhile, a US naval blockade of the Iranian ports has drastically restricted its oil and other trade.

The MoU, which had ended the months-long military hostility, collapsed after 60 days due to disputes over who had ultimate control over the Strait of Hormuz, which Iran has used as leverage in the war against the United States. Oil tankers have become the latest targets in the US-Israel war on Iran, with Tehran repeatedly warning vessels against using unauthorised routes through the Strait of Hormuz amid reports that a growing number of oil tankers are passing through the waterway.

Prior to the start of the war, 20 percent of the world’s oil and gas supplies flowed through the strait. So, where exactly will Iran’s proposed zone be, what restrictions will apply, and how does Tehran intend to enforce this? What did Iran say about the restrictive zone?

Iran’s Supreme National Security Council Secretary Mohsen Rezaei said the zone would be announced in the coming days. “This zone will start from the US Navy’s blockade line and include areas of the Persian Gulf,” he said, according to Iranian state media.

“Any ship entering this new zone will be placed on the sanctions list [of Iran].” Rezaei said the zone would “begin from the line of the US naval blockade, extend toward the Strait of Hormuz, and from this side continue into the Persian Gulf”. However, Tehran has provided few details about the zone’s precise boundaries or what being placed on its sanctions list would mean for vessels entering it.

Rezaei said new maps detailing routes, worked on in conjunction with Oman for the Hormuz Strait, would also be approved soon. “The maps of a new international corridor which lies in Iranian and Omani waters and in which Iran will have management have been agreed and should be signed in the coming days,” he added.

“We will only commit to the Strait of Hormuz being open when they [the Americans] stop the sabotage, threats and attacks on Iran.” The announcement comes after Deputy Foreign Minister Kazem Gharibabadi said late last month that Iran and Oman had agreed on a temporary maritime route for ships travelling through the Strait of Hormuz, whose entry “would be through our territorial waters, and part of the exit route would also be through our territorial waters”.

How have the US and the world reacted? There has been no immediate US or wider international response specifically to Rezaei’s announcement of the new zone. However, on Sunday, Washington rejected an Iranian claim reported in local media that a US vessel had attempted to enter an area Tehran considers restricted and was attacked.

US Central Command (CENTCOM) spokesperson Captain Tim Hawkins called the Iranian account “a total lie”. The alleged attack comes days after Washington targeted three Iranian oil tankers and Tehran hit tankers and fired a ballistic missile towards US warships patrolling near the Strait of Hormuz.

Doesn’t Iran already prescribe a route for ships through Hormuz? Yes. Iran is already demanding that vessels use routes it approves through the strait. Iran first published a map of its approved navigation routes in April, directing vessels much closer to the Iranian coastline than they travelled before the war.

The route currently authorised by it follows a corridor along Iran’s coast. But Iran’s attempt to control navigation has been challenged by a separate route closer to Oman. In June, Oman, working with the International Maritime Organization (IMO), a United Nations agency that oversees shipping at sea, laid out a southern corridor intended to restore safe navigation through the strait.

A Liberian-flagged tanker, the Stoic Warrior, subsequently used a route that took it close to the coasts of the United Arab Emirates and Oman before passing around the Musandam Peninsula, an Omani exclave. The Islamic Revolutionary Guard Corps (IRGC) objected to it, declaring that “the only authorised route” was the one announced by Iran and warning that vessels crossing without its permission would be “unacceptable and extremely dangerous”.

Following the 14-point MoU signed in June in the Swiss city of Geneva, traffic in the strait had picked up. But the resumption of attacks has severely limited commercial shipping in and around the key waterway. Under the MoU, the US agreed to end its naval blockade within 30 days, while Iran pledged to clear mines from the Strait of Hormuz and allow ships to pass “with no charge” for 60 days.

What is the current status of traffic in the Strait of Hormuz? Traffic is still getting through, but at substantially reduced levels. Before the conflict, about 20 million barrels of crude oil per day flowed through the waterway. US Energy Secretary Chris Wright, speaking to media on Sunday, said current transits were averaging more than nine million barrels of oil per day.

When pipelines bypassing the strait are included, Wright said flows were probably at “two-thirds or more of pre-conflict flows”. “So Iranians are still causing trouble, but the United States Navy is winning that battle,” he said. Bolstering US claims was the United Kingdom Maritime Trade Operations (UKMTO) Centre, which on Sunday said 59 ships passed through the Strait of Hormuz in the previous 48 hours.

US President Donald Trump has repeatedly claimed that the waterway is under Washington’s control despite near-daily Iranian attacks on ships, going so far as to suggest renaming the Strait of Hormuz after himself. Iran has disputed claims of growing traffic, claiming its chokehold on the waterway continues.

However, recent data from other maritime tracking companies and websites paints a mixed picture. Figures show only six vessels crossed the strait on Wednesday, 11 on Tuesday and five last Monday, with a 10-day average of just 13 vessels per day. On Monday, marine analytics firm Kpler showed that an average of 10 commodity ships transited the strait per day over the past 10 days, the lowest since May.

Before the US and Israel launched the war on Iran on February 28, more than 130 ships passed daily through the strait, which allowed free navigation. Now, the Trump administration is negotiating with Iran to open the strait. Meanwhile, Iran’s nuclear programme, which Trump and Israeli Prime Minister Benjamin Netanyahu invoked to launch the war, has vanished from the headlines.

Can Iran militarily enforce a new zone? Tehran has so far demonstrated an ability to make passage through Hormuz dangerous, forcing ships to avoid the waterway. At least 19 seafarers have been killed and dozens of ships attacked since March. Whether it can militarily enforce the much broader zone Rezaei has proposed – particularly against vessels protected by the US military – remains to be seen.

Stephen Zunes, founding chair of Middle Eastern Studies at the University of San Francisco, says Iran will struggle to enforce a restricted zone near the Strait of Hormuz. “It’s hard to see how they will really be able to enforce it. Iranian ships and planes trying to enforce that would be very vulnerable to US attacks,” he told Al Jazeera.

“But perhaps they are giving a warning, given there still would be some risk for shipping companies to not count on being able to get through the strait without suffering consequences.” Zunes said Iran may be hoping to provoke a broader US military response, which could benefit Tehran politically by “justifying attacks” on neighbouring Gulf countries and US military facilities in the region.

That, in turn, could help Iran, as public opinion in the US seems against continuing the conflict, while pushing the Iranian public to “rally around the flag” amid growing economic hardship at home. Moreover, Zunes noted, Iran’s plan for a restricted zone could be linked to its pending deal with Oman on shipping routes through the waterway.

If the deal with Oman is workable and something the US can accept, Iran could “pull back” from enforcing the restricted zone, Zunes said. If not, then Tehran has “something ready to try to make it more problematic for Washington” to refuse the deal with Oman.

Iranian Supreme National Security Council Secretary Mohsen Rezaei stated that Tehran intends to designate a new restricted shipping zone in the Persian Gulf, though details regarding the specific geographic boundaries and enforcement mechanisms of this declared area remain unverified.

This announcement follows recent escalations, including US airstrikes and Iranian missile attacks, amid conflicting claims from both governments regarding the current operational status of the Strait of Hormuz.

Iranian state media reported that IRGC ballistic missiles targeted two US warships in the Strait of Hormuz, alleging damage that forced them to withdraw, though these claims have not been independently verified. These actions followed US military strikes on three Iranian oil tankers, which Washington described as part of an IRGC-linked funding network.

The exchange of fire appears to be driven by tit-for-tat retaliation, with both sides attributing the conflict to prior attacks on their respective military and economic assets.