CNN — A cargo ship that was struck by a Houthi ballistic missile on Monday has created an 18-mile long oil slick in the Red Sea as it continues to take on water, two US officials said Friday.

The M/V Rubymar — a Belize-flagged, UK-registered, Lebanese-owned vessel — was carrying 41,000 tons of fertilizer when it was struck on Monday by one of two ballistic missiles fired from Houthi territory in Yemen.

US Central Command said the ship is currently anchored as it takes on water. “The Houthis continue to demonstrate disregard for the regional impact of their indiscriminate attacks, threatening the fishing industry, coastal communities, and imports of food supplies,” US Central Command said.

One of the US officials said the threat of more Houthi attacks in the Red Sea, combined with the condition of the water, makes it incredibly difficult to safely get to the ship and attempt to tow it to a port.

The damage sustained by the Rubymar is potentially the most significant to a vessel caused by an attack launched by the Houthis, who have been targeting commercial shipping in the Red Sea and Gulf of Aden for months.

It remains unclear what kind of substance is causing the slick.

US Central Command said this week that the Rubymar sent out a distress call after the attack and was assisted by a coalition warship and another merchant vessel, which took the crew to a nearby port. It appeared to be the first time a crew has been forced to evacuate a ship after it was hit by the Houthis. Many of the ships struck by Houthi missiles have been able to continue their voyage.

Deputy Pentagon Press Secretary Sabrina Singh said Thursday that the Rubymar was “taking on water as we speak.”

“It’s creating an environmental hazard with the leakage of all the fuel that it’s carrying,” Singh said. “On top of that, it was carrying, to my understanding, fertilizer. So the Houthis are creating an environmental hazard right in their own backyard.”

CNN reported on Friday that the Biden administration is struggling to stop the ongoing attacks by the Houthis against ships in the Red Sea, and the group is continuing to fortify its weapons stockpile inside Yemen, even though the US has carried out significant strikes on the group in recent weeks.

The Houthis’ attacks have been ongoing for months, and despite several rounds of strikes by the US and UK on their capabilities, US officials told CNN it’s unclear how much weaponry the militia group still has.

“The US campaign against the Houthis appears to bear the hallmarks of many of these highly circumscribed, scrubbed campaigns of the past where we seek to avoid causing them actual pain,” a former US military official told CNN.

The Houthis’ attacks have increased in recent days; Singh said Thursday there has “certainly” been “an increase in attacks from the Houthis” over the last 72 hours. And while the Houthis have said they are conducting the attacks in support of the Palestinian people and targeting ships connected to Israel, many of the vessels attacked have instead been connected to other countries.

One other ship hit by the Houthis on Monday — the M/V Sea Champion, a US-owned, Greek-flagged bulk carrier — was carrying grain to Yemen. A CENTCOM release on the attack said the Sea Champion has “delivered humanitarian aid to Yemen 11 times in the past five years.”

“So, again, they’re saying that they’re conducting these attacks against ships that are connected to Israel,” Singh said Thursday. “These are ships that are literally bringing goods, services, aid to their own people, and they’re creating their own international problem.”

This story has been updated with additional developments.