LONDON/OSLO — An unmanned Iranian boat skips over the waves at full speed and rams into a US aircraft carrier, sending up an orange fireball and plumes of smoke.

That attack against a mock-up US warship was part of elaborate naval war games carried out by the elite Revolutionary Guards in 2015. Dozens of speedboats, ships firing missiles, and helicopters were involved. Video of the exercise ran on state TV for hours.

US officials are now concerned that Iran has passed this naval combat expertise on to proxy forces in the region, whom Washington blames for attacks against four oil tankers off the coast of the United Arab Emirates on Sunday.

If Iran or one of its proxies was involved in the tanker attacks, which did not sink any of the ships or cause fatalities, it was a warning message, experts say.

“Iran’s actions are conducted in a manner which are both understood by the world to be conducted by Iran, but not to the extent that the international community can justify a response. In this way, the actions are attributable but deniable,” said Norman Roule, a former senior CIA officer with experience in Middle East issues.

Meanwhile, London’s marine insurance market has extended the list of waters deemed high risk to include Oman, the United Arab Emirates and the Gulf after ship attacks off Fujairah, officials said on Friday, in a move that could push up premiums.

The London insurance market’s Joint War Committee said in a statement that the additions cover areas of perceived enhanced risk for marine insurers and reflected enhanced regional risk.

“The situation will be kept under close review,” said the Joint War Committee, whose guidance influences decisions by underwriters on insurance premiums.

The Joint War Committee, made up of syndicate members from the Lloyd’s Market Association (LMA) and representatives from the London insurance company market, normally meets every quarter to review areas it considers high risk for merchant vessels and prone to war, terrorism, piracy and related perils.

The Joint War Committee, which met on Thursday after developments in the Middle East ahead of Friday’s decision, also added adjacent waters around the Gulf of Oman to its high risk list. The last update to the list was in June 2018.

The UAE, Saudi Arabia and Norway have launched an investigation and have described the attacks as deliberate. They have not blamed anyone.

A confidential Norwegian insurers’ report seen by Reuters concluded that Iran’s elite Revolutionary Guards (IRGC) were “highly likely” to have facilitated the attacks on the tankers.

The assessment issued this week by the Norwegian Shipowners’ Mutual War Risks Insurance Association (DNK) concluded that the attack was likely to have been carried out by a surface vessel operating close by that dispatched underwater drones carrying 30-50 kg (65-110 lb) of high-grade explosives to detonate on impact.

The DNK based its assessment that the IRGC was likely to have orchestrated the attacks on a number of factors, including: A high likelihood that the IRGC had previously supplied its allies, the Houthi militia fighting the internationally-recognized government in Yemen, with explosive-laden surface drone boats capable of homing in on GPS navigational positions for accuracy. The similarity of shrapnel found on the Norwegian tanker to shrapnel from drone boats used off Yemen by Houthis, even though the craft previously used by the Houthis were surface boats rather than the underwater drones likely to have been deployed in Fujairah.

The DNK report said the attacks had been carried out between six and 10 nautical miles off Fujairah, which lies close to the Strait of Hormuz. Iran has in the past threatened to block all exports through the Strait of Hormuz, through which an estimated fifth of the world’s oil passes. According to DNK, it was highly likely that the attacks had been intended to send a message to the United States and its allies that Iran did not need to block the Strait to disrupt freedom of navigation in the region. DNK said Iran was also likely to continue similar low-scale attacks on merchant vessels in the coming period. — Reuters