Iran's Revolutionary Guards (IRG) are "highly likely" to have had a role in sabotaging four tankers off Fujairah in the United Arab Emirates last Sunday, according to Reuters reports.
The hulls of tankers owned by interests in Saudi Arabia, UAE and Norway were damaged by explosives in the attack this week.
A confidential report from the Norwegian Shipowners' Mutual War Risks Insurance Association (DNK), seen by Reuters, says the attack is likely to have been carried out by underwater drones.
The DNK believes the drones were carrying 30-50 kg of high-grade explosives to detonate on impact and were likely dispatched by a nearby surface vessel.
In its report, cited by Reuters, the DNK said its conclusions were based on the high likelihood that the IRG had previously supplied its allies in Yemen with similar drone boats.
Such vessels are capable of homing in on GPS navigational positions, Reuters reported.
Shrapnel found on the Norwegian tanker is similar to shrapnel from drone boats used off Yemen by the Iran-backed Houthi militia in Yemen, the DNK said.
The insurer believes the attacks were intended to send a message to the United States and its allies that Iran does not need to block the Strait of Hormuz to disrupt vessel traffic in the region, the newswire said.
Before the attack, Iran and the IRGC had recently threatened to use military force and were highly likely to choose "asymmetric measures with plausible deniability" against their stronger foe, Reuters said, quoting from the DNK report.
The damaged vessels are the Bahri-owned 299,000-dwt VLCC Amjad (built 2017); an 105,000-dwt aframax Al Marzoqah (built 1999), operated by Red Sea Marine Services of Dubai; plus the 47,000-dwt crude tanker Andrea Victory (built 2005), managed by Thome of Norway.
The UAE-flagged bunker vessel A.Michel also sustained damage to its engine room in the attack, according to reports.
The Norwegian Maritime Authority raised the security level for its ships following the attack.
However, tanker owners are unlikely to be the victims of a wider campaign of terror in the Arabian Gulf, UK security consultant Dryad Maritime has said.
