Middle East. File Image / AI Generated

• UKMTO Warning 133-26: four unknown projectiles hit two vessels 4 nm west of Khasab, Oman
• One vessel on fire, status of the second unknown; reported by the master of a third ship 6 nm away
• Vessels involved not yet identified; authorities investigating
• Follows the Hercules Star attack off Dubai that killed a seafarer, US strikes on five Iranian tankers, and an IRGC claim to have fired on eight tankers on Wednesday

Two vessels have been hit by projectiles off Khasab, Oman, at the entrance to the Strait of Hormuz, with one of them set on fire, the UK Maritime Trade Operations (UKMTO) reported on Thursday.

The master of a third vessel reported seeing four unknown projectiles strike two unknown vessels about 6 nm north of his position, causing a fire on one of them, and was unsure of the status of the second, UKMTO said in Warning 133-26, placing the incident 4 nm west of Khasab.

"Authorities are investigating," the agency said, advising vessels to transit with caution and to report any suspicious activity.

UKMTO gave no vessel names or types, and no information on casualties.

Khasab sits on Oman's Musandam peninsula, on the southern side of the strait's narrowest point, and the waters around it have seen repeated attacks since late August, including a tanker struck by three projectiles 17 nm east of the port on August 31 while completing an outbound transit.

About an hour before the UKMTO report was circulated, Iran's Revolutionary Guards said they had targeted a Saildrone Explorer unmanned surface vessel in the strait, with Tasnim news agency publishing images said to show it on fire, according to Iran International.

The US military gave no immediate confirmation.

The latest incident caps a week of escalation in and around the Gulf.

On Wednesday Peninsula confirmed that one seafarer had been killed and another was missing after the bunker tanker Hercules Star, which it had chartered, was hit at anchor off Dubai in what maritime security sources assessed as a drone strike, prompting IBIA to call for greater protection of seafarers.

The US, meanwhile, struck five Iranian crude tankers in the Gulf of Oman and near Kharg Island on Tuesday after what it said were two failed missile attacks on a US Navy warship, following strikes on three others the previous week.

Iran's Revolutionary Guards said on Wednesday that they had retaliated by firing on two US vessels and eight oil tankers attempting to cross an area of the strait Iran has declared prohibited, and by launching ballistic missiles at a base used by US forces at Al-Azraq in Jordan, where 18 of 20 missiles were intercepted, according to Reuters, which called it the biggest declared wave of attacks on shipping by either side since the war began.

UKMTO said the same day that several merchant vessels in the northern Gulf and the Gulf of Oman had been hit by disabling fire overnight, including a cargo ship struck by a projectile about 52 km southeast of al-Faw, Iraq, while US Central Command said no US warship had been struck and all the IRGC's attempted attacks had failed.

Commercial transits through the strait had already fallen to their lowest level since May, at around ten ships a day over the ten days to Sunday, according to LSEG data cited by maritime analysts, with no VLCC having left the Gulf for almost a week.

Brent crude rose above $106/bbl on Thursday.