The cost of coverage has leaped to about 5% of the value of a ship, roughly five times the level seen in the earliest days of the Iran war.

Insurance might help, but shipowners and crews are still nervous about using the vital waterway until hostilities cease.

The move may discourage ship owners from loading cargoes within the Persian Gulf, which is the source of about a fifth of the world's supply of crude.

Some ships have been adopting new ways to avoid attack, though they haven't all been successful.

Insureds are increasingly turning to Russian providers backstopped by a heavily sanctioned, state-backed reinsurer.

Underwriters are now charging between 0.75% and 1% of the value of the ship to sail through the region.

Russian oil has been trading above $60 a barrel in Asia for much of this year, raising the prospect of violations for insurers in G-7 nations.

At least 12 of the 13 members of the International Group of P&I Clubs have changed policies to exclude claims stemming from Russia's invasion of Ukraine.