(Bloomberg) -- A tanker operated on behalf of trading giant Trafigura Group that was carrying a cargo of Russian fuel was struck by a missile as it left the Red Sea, in the most significant attack yet by Yemen’s Houthi rebels on an oil-carrying vessel.

“Firefighting equipment on board is being deployed to suppress and control the fire caused in one cargo tank on the starboard side,” a Trafigura spokesperson said Friday in a statement. “We remain in contact with the vessel and are monitoring the situation carefully. Military ships in the region are underway to provide assistance.”

Yemen’s Houthi rebels claimed the strike on the Marlin Luanda. The vessel is carrying Russian-origin naphtha — a product used to make plastics and gasoline — purchased below the price cap imposed by the Group of Seven nations, the Trafigura spokesperson also said.

Global benchmark Brent rallied to a two-month high.

The attack will raise fresh questions about whether oil tankers will continue to transit the Red Sea. Since joint US and UK airstrikes on the Houthis earlier this month, tanker traffic in the region has declined but some oil exporters, including Saudi Arabia, continue to use the waterway.  

Read more: How Red Sea Crisis Raises Supply Chain Worries Anew: QuickTake

That the targeted ship carried fuel from Russia will likely concern Moscow. Vast amounts of Russian petroleum now pass through the southern Red Sea to reach Asian buyers following Europe’s shunning of its cargoes due to the war in Ukraine. A Houthi spokesman previously told the Russian newspaper Izvestia that Russian and Chinese ships sailing through the Red Sea would be safe even as the group targets US and UK vessels. 

The vessel collected its Russia-origin cargo via a so-called ship-to-ship transfer from a stretch of water in the Laconian Gulf in southern Greece, according to data from analytics firm Kpler. The area has been pivotal in helping Russia to get its petroleum to the global market and, as well as handling supplies under the price cap, has also facilitated more shadowy trades.

Trafigura, along with other commodity traders like Glencore Plc, Vitol Group and Gunvor Group, was one of the biggest lifters of oil from Russia before the country’s full-scale invasion of Ukraine and was a partner in a major oil project run by state producer Rosneft PJSC.

The company has since moved away from those flows following US, European and UK sanctions on Russia’s energy exports. While its CEO Jeremy Weir has said it continues to trade small amounts of refined oil products from Russia, that position was under review.

That the company picked up a cargo via ship-to-ship transfer off the coast of Greece sheds light on how one of the world’s biggest commodity trading houses is resorting to less-than-transparent means as it continues to facilitate the export of oil products from Russia, at a time when war in Ukraine is still raging.

READ: Saudi Keeps Sending Oil Through Houthi-Menaced Red Sea

The latest incident also suggests that the US and its allies still haven’t sufficiently degraded the Houthis’ military capabilities two weeks after launching the first of several airstrikes on the group’s missiles, radars and other assets across Yemen. Last weekend, US Deputy National Security Advisor Jon Finer said military actions to deter the Houthis and other groups backed by Iran would take time.

“Deterrence is not a light switch,” Finer told ABC. “We are taking out these stockpiles so they will not be able to conduct so many attacks over time. That will take time to play out.”

In its update on the incident, the UK Navy said the vessel remained ablaze and that coalition warships were attending the scene. It advised ships to transit with caution.

The area in question and the southern Red Sea have been the center of multiple attacks on ships by Houthi militants in recent weeks. Since mid-November, the Houthis have launched near daily attacks on vessels transiting the waterway, in an act of solidarity with Palestinians amid the war between Israel and the militant group Hamas. The conflict has rerouted trade flows as some shippers avoid the key waterway.

Read more: How Houthi Red Sea Attacks Are Disrupting World Trade: QuickTake

Earlier Friday, missiles exploded near a Panama-flagged, India-affiliated ship carrying barrels from Russia, according to Ambrey.

(Updates with details throughout)

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