A secret insurance industry report has found Iran’s Revolutionary Guards are ‘highly likely’ to have been behind a submarine drone attack on tankers in the Gulf.

Last Sunday four tankers, including two Saudi ships off Fujairah in the United Arab Emirates were damaged, amid flaring tensions over Washington’s sanctions on Tehran.

Analysis of shrapnel fragments has found the assault was likely carried out by a boat operating close by which released underwater drones carrying 65-110lbs of high-grade explosives to detonate on impact.