WASHINGTON (AP) The U.S. and Britain struck 18 Houthi targets in Yemen on Saturday, answering a recent surge in attacks by the Iran-backed militia group on ships in the Red Sea and Gulf of Aden, including a missile strike this past week that set fire to a cargo vessel.

According to U.S. officials, American and British fighter jets hit sites in eight locations, targeting missiles, launchers, rockets, drones and air defense 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 U.S. and British militaries have conducted a combined operation against the Houthis since Jan. 12. But the U.S. 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 U.S. 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 worlds most critical waterways, said U.S. Defense 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 defense of our country, our people and our nation, it said in a statement.

The U.S., U.K., and other allies said in a statement the necessary and proportionate strikes specifically targeted 18 Houthi targets across 8 locations in Yemen that also included underground storage facilities, radar and a helicopter.

U.K. Defense Secretary Grant Shapps said RAF Typhoon jets engaged in precision strikes aimed at degrading Houthi drones and launchers. Shapps said it came after severe Houthi attacks against commercial ships in the Red Sea and Gulf of Aden, including against the British-owned MV Islander and the MV Rubymar, which forced the crew to abandon ship. Its the fourth time Britain has joined in the U.S.-led strikes.

The strikes have support from the wider coalition, which includes Australia, Bahrain, Canada, Denmark, the Netherlands and New Zealand.