LONDON/ADEN: The cost of insurance for ships sailing through the Red Sea has nearly doubled after Yemen’s Houthis attacked a tanker that appears to be leaking oil, with environmental fears growing for trade route, industry sources said on Wednesday.

Iran-aligned Houthi militants first launched aerial drone and missile strikes on the waterway in November in what they say is solidarity with Palestinians in Gaza. In over 70 attacks, they have sunk two vessels, seized another and killed at least three seafarers.

In the latest escalation, the Greek-flagged Sounion tanker was attacked last week by multiple projectiles and appears to be leaking oil, the Pentagon said on Tuesday.

A third party had tried to send two tugs to help salvage the Sounion, but the Houthis threatened to attack them, the Pentagon added.

Insurance industry sources, speaking on condition of anonymity, said on Wednesday additional war risk premiums, paid when vessels sail through the Red Sea, were quoted up to 0.75% of the vessel from 0.4% before the attack, although they were higher at 1% in February according to industry assessements of levels of risk.

The latest upsurge in cost can add up to hundreds of thousands of dollars for a voyage through region, although rates for Chinese-owned vessels have been up to 50% lower since February due to less risk of being targets, sources added.

One industry source said some underwriters were currently not providing cover through the region because of the potential risk of the tanker sinking.

An official with the European Union’s Aspides naval mission cited a letter sent on Aug. 28 to maritime rescue coordination centres, saying it was assessing the “feasibility of protective measures” such as towing the Sounion. “This situation poses a serious and imminent threat of regional pollution, with coastal states at the highest risk,” the letter said.