The UN’s International Maritime Organization (IMO) has paused the planned evacuation of more than 11,000 sailors stranded in the Strait of Hormuz after a cargo ship passing through the waterway was attacked.

IMO chief Arsenio Dominguez said several boats had already been evacuated, but the agency wanted to ensure that “necessary safety guarantees” would continue to be in place.

The British maritime security agency UKMTO reported on Thursday that a ship had been struck 7.5 nautical miles southeast of Oman’s port of Dahit by “an unknown projectile”. No casualties were reported.

The attack came after Iran’s Islamic Revolutionary Guard Corps (IRGC) had warned that attempts to cross the strait along a route designated by the IMO would be “unacceptable and completely dangerous” and vessels should coordinate with Iran.

US officials said Iran had fired on the ship, according to US media reports.

Maritime risk management firm Vanguard said the ship, the Singapore-flagged Ever Lovely, continued through the strait despite the attack.

The Ever Lovely was leading a flotilla of four other ships and followed a southern route identified by the IMO on Thursday morning, the Wall Street Journal reported, citing ship-tracking website MarineTraffic.

There was no warning from the Iranian navy to the ships on radio, according to seafarers in the flotilla who spoke to the paper.

IMO chief Dominguez said in a statement on Thursday that the vessel that was attacked “did not transit under IMO’s evacuation framework”.

“I have always reiterated that the safety of the seafarers remains paramount. Therefore, to ensure a coordinated approach and navigational safety, the evacuation plan will be paused until further clarity is obtained,” he said.

Hundreds of ships and thousands of sailors have been stranded in the Gulf since February because of the US-Israel war against Iran.

The UN evacuation effort was announced on Tuesday following the reopening of the strait, with Dominguez saying the “large-scale operation” had the cooperation of Iran, Oman, the US, other coastal states in the region and the maritime industry.

The attack came after the body set up by Iran to manage the strait said vessels passing outside designated routes would not be guaranteed safe passage.

In a post on X, the Persian Gulf Strait Authority (PGSA) said: “Any consequences arising from the use of unauthorised routes shall be the responsibility of the vessel’s owner, operator and master”.

Last week the US and Iran agreed to end hostilities under a 14-point deal – which also called for Iran to use its “best efforts for the safe passage of commercial vessels with no charge for 60 days”.

However, Tehran has repeatedly said it plans to charge what it calls maritime service fees for crossing the strait, as opposed to tolls.

The plan is fiercely opposed by the US, with Secretary of State Marco Rubio warning on Tuesday that no country is allowed to impose tolls on the Strait of Hormuz, which he called “an international waterway”.

Rubio is currently in Bahrain as part of a tour of the Gulf to discuss the deal with Tehran.

After US and Israeli attacks against Iran began at the end of February, Tehran effectively closed the strait – a critical waterway for oil and gas shipments – causing a spike in global oil prices and choking off shipments of other crucial commodities such as fertiliser.

However the cost of crude has been moving sharply lower since the US and Iran signed a Memorandum of Understanding (MOU) on 17 June, which set out a 60-day period for negotiations on Tehran’s nuclear programme and other measures to end the war.

Earlier on Thursday, the price of oil briefly fell below $72.48 (£55) a barrel, the price it was at the day before the US and Israel launched attacks on Iran, before edging up to $73.23.