The US and UK said they hit 18 Houthi targets in Yemen on Saturday, after a recent surge in attacks by the Iran-backed militia group, writes Euronews.

According to US officials, American and British fighter jets hit sites in eight locations, targeting missiles, launchers, rockets, drones and air defence systems. The officials spoke on condition of anonymity in order to provide early details of an ongoing military operation.

This is the fourth time that the US and British militaries have conducted a combined operation against the Houthis since Jan. 12. But the US has also been carrying out almost daily strikes to take out Houthi targets, including incoming missiles and drones aimed at ships, as well as weapons that were prepared to launch. The US F/A-18 fighter jets launched from the USS Dwight D. Eisenhower aircraft carrier, which is currently in the Red Sea, officials said.

“The United States will not hesitate to take action, as needed, to defend lives and the free flow of commerce in one of the world’s most critical waterways,” said US Defence Secretary Lloyd Austin. “We will continue to make clear to the Houthis that they will bear the consequences if they do not stop their illegal attacks.”

The Houthis denounced the “US-British aggression” and vowed to keep up its military operation in response. “The Yemeni Armed Forces affirm that they will confront the US-British escalation with more qualitative military operations against all hostile targets in the Red and Arabian Seas in defence of our country, our people and our nation,” it said in a statement.