A Houthi ballistic missile attack on a commercial ship in the Gulf of Aden resulted in at least two fatalities among the crew members, two US officials told CNN, marking the first time that the Iran-backed militant group has killed anyone as part of their ongoing attacks on ships transiting the Red Sea.

The attack struck the M/V True Confidence, a Barbados-flagged, Liberian-owned bulk carrier, the officials said. The ship has since been abandoned and coalition warships are now in the area assessing the situation, the officials said. At least six other crew members were injured, one of the officials said.

The attack happened around 11:30 am Sana’a time, or around 3:30 a.m. ET, one of the officials said. The strike marks a significant escalation of the Houthi attacks on Red Sea shipping, which began in October in response to Israel’s war in Gaza.

The Houthis have launched more than 45 missile and drone attacks against commercial and US and coalition Naval vessels operating in the Red Sea, according to US and western officials, most of which have been intercepted by US or coalition destroyers or landed harmlessly in the water.

To date, no military vessels have been impacted by Houthi UAVs or missiles, according to Defense Department spokesperson Maj. Pete Nguyen. But more than a dozen commercial ships, including several US vessels, have been hit since October, Nguyen said.

The US and UK have also carried out four rounds of strikes against Houthi targets inside Yemen since January, hitting targets including weapons storage facilities, missile storage facilities, one-way attack unmanned aerial systems, air defense systems, radars, and helicopters used by the rebel group.

US Central Command forces have also been regularly conducting dynamic strikes against Houthi missiles seen preparing to launch from inside Yemen.

The Biden administration has been struggling to stop the attacks, however, and the group has been continuing to fortify its weapons stockpile inside Yemen, CNN previously reported.

Multiple officials told CNN that the US still does not have “a denominator” that would allow them to assess the percentage of Houthi equipment the US and UK have actually destroyed in airstrikes, and it is not clear whether the US will shift its military approach further.

“We know that the Houthis maintain a large arsenal,” Deputy Pentagon press secretary Sabrina Singh said last week, hours after the Houthis hit yet another cargo vessel in the Gulf of Aden with ballistic missiles. “They are very capable, they have sophisticated weapons, and that’s because they continue to get them from Iran.”

“They continue to surprise us,” said one senior defense official, referring to the Houthis. “We just don’t have a good idea of what they still have.”

And despite a robust US and coalition presence in the Red Sea, which includes the USS Dwight D. Eisenhower aircraft carrier and several US destroyers, the Houthi attacks have caused a massive drop in ships traveling through the Suez Canal.

The passage links the Red Sea with the Mediterranean Sea, allowing ships to cut thousands of miles off shipping routes instead of sailing around Africa. In the first half of February, the Suez Canal experienced a 42% drop in monthly transits and an 82% decrease in container tonnage from its peak in 2023, according to the United Nations.