By Oren Liebermann and Haley Britzky, CNN

(CNN) — The United States and the United Kingdom carried out strikes against an array of Houthi targets in Yemen, according to two US officials, marking the fourth time the international coalition has launched a combined attack on the Iran-backed rebel group.

The strikes hit 18 targets across eight locations, according to a statement from the coalition, including underground weapons storage facilities, missile storage facilities, one-way attack unmanned aerial systems, air defense systems, radars, and a helicopter.

Four Royal Air Force Typhoon fighter jets, supported by two Voyager tankers, participated in the coalition strikes, the British Ministry of Defence said in a statement late Saturday.

This latest round of strikes comes after the Pentagon acknowledged that the Houthis have recently carried out more attacks on commercial shipping in the Red Sea and the Gulf of Aden – some of the world’s most critical waterways. On Thursday, Pentagon deputy press secretary Sabrina Singh said there had been “an increase in attacks from the Houthis, more consistency” over the past several days.

Those attacks – which the Houthis say are in solidarity with Palestinians amid Israel’s war against Hamas in Gaza – 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.

The Houthis have carried out more than 45 attacks on commercial and naval vessels in the region since mid-November, according to the coalition statement, which called them “a threat to the global economy” that demands an international response.

“We know that the Houthis maintain a large arsenal,” Singh said Thursday, 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.”

That attack was one of a series of successful Houthi missile launches against commercial shipping in recent days, many of which have hit vessels with ties to the US and the UK.

Houthi rebels confirmed Sunday local time on social media that they used missiles to target an American oil tanker in the Gulf of Aden on Saturday.

Houthi spokesperson Yahya Saree did not comment on whether the missile attack resulted in a hit on the tanker, the M/V Torm Thor, but US forces said earlier they had successfully shot down at least one missile that had been launched into the Gulf of Aden. Saree also said Houthi forces targeted a number of American warships in the Red Sea with unmanned aerial vehicles.

In another recent example, the M/V Rubymar, a Belize-flagged, UK-registered vessel that was hit by a Houthi ballistic missile Monday, appeared to become the first case in which the crew had to abandon ship. On Friday, US Central Command said the ship was taking on water in the Red Sea as it created an 18-mile oil slick.

The US has tried to disrupt the Houthi’s ability to target commercial and US warships by going after their primary weapons, including anti-ship cruise missiles and ballistic missiles, as well as one-way attack drones. The US has also destroyed maritime drones and underwater drones.

Earlier this month, the Pentagon said the continued strikes against Houthi targets in Yemen, which began in January, have destroyed more than 100 missiles and launches, including anti-ship missiles, drones, radars and more.

But the continued strikes have done little to stem the tide of Houthi attacks, with some inside the administration now arguing that the use of force alone is not working. It is also extremely expensive and impractical, some officials note, to keep firing multimillion-dollar missiles at cheap Houthi drones and missiles.

Part of the challenge is in knowing how much weaponry the Houthis possess. Multiple officials have told CNN that the US still does not have “a denominator” that would allow them to assess the percentage of Houthi equipment they have destroyed, and it is not clear whether the US will shift its military approach further.

“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.”

Even so, the US and the international coalition have shown no signs of backing down, warning the Houthis that the strikes will continue if the attacks on international shipping don’t come to an end.

“Our aim remains to de-escalate tensions and restore stability in the Red Sea, but we will once again reiterate our warning to Houthi leadership: we will not hesitate to continue to defend lives and the free flow of commerce in the face of continued threats,” the coalition statement said.

CNN’s Jonny Hallam, Hande Atay Alam and Jomana Karadsheh contributed to this report.