Yemen’s Houthi rebels on Friday stepped up attacks on vessels transiting the Red Sea, including a hit that sparked a fire on a fuel tanker operated on behalf of trading firm Trafigura.

Trafigura said a missile struck the fuel tanker Marlin Luanda as it transited the Red Sea. The tanker was carrying Russian naphtha purchased below the price cap in line with G7 sanctions, a Trafigura spokesperson said.

Firefighting equipment on board was being deployed to suppress and control a fire in one cargo tank on the starboard side, the company said in an emailed statement.

“We remain in contact with the vessel and are monitoring the situation carefully,” it said, adding military ships were underway to assist.

Attacks by Houthi rebels have primarily targeted container vessels moving through the Red Sea. Many oil tankers have kept using the route.

On Friday, vessel Free Spirit, chartered by Vitol to carry crude oil, did a U-turn before reaching the Gulf of Aden, shortly after the attack on the Marlin Luanda, according to data from LSEG.

A representative for Vitol did not immediately respond to a request for comment. Earlier, the United Kingdom Maritime Trade Operations (UKMTO) agency and British maritime security firm Ambrey said they had received reports of vessels being struck in the Red Sea near Yemen’s Aden and a fire breaks out aboard.

The Houthi military spokesperson said naval forces carried out an operation targeting the “British” tanker Marlin Luanda in the Gulf of Aden, causing a fire to break out.

UKMTO received a report of an incident approximately 60 nautical miles southeast of Aden where “a vessel has been struck by a missile and remains on fire.” Crew members were reportedly safe.

“Coalition Warships are in attendance and supporting the vessel,” UKMTO added. Ambrey also said it was aware of an incident 55 miles (88.5 kilometres) southeast of Aden where a fire broke out after a merchant vessel was hit by a “missile”.

Earlier, UKMTO reported an incident in which two missiles exploded in waters near a ship off the port of Aden and another one 60 nautical miles off Yemen’s Hodeidah port. It was unclear if one of those vessels was the Marlin Luanda.

The U.S. military said in a statement it shot down an anti-ship ballistic missile from a Houthi-controlled area of Yemen, adding there were no injuries or damage.

Yemen’s Iran-aligned Houthi militants have launched waves of exploding drones and missiles at vessels since Nov. 19, in response to Israel’s military operations in Gaza. Some shipping companies have suspended transits through the Red Sea and taken much longer, costlier journeys around Africa.

U.S. and British warplanes, ships and submarines have launched dozens of retaliatory air strikes across Yemen against Houthi forces.