The U.S. and United Kingdom conducted strikes on 18 Houthi targets in Yemen as the terrorist group’s attacks on commercial shipping and naval vessels escalated, the countries said in a statement Saturday.

Saturday’s strikes are the fourth large-scale combined attacks involving the U.S. and U.K., as well as non-operational support from at least six other nations, on Houthi assets in Yemen the rebel group uses to terrorize Red Sea shipping. They targeted 18 targets at eight different locations in Yemen, including underground weapons and missile storage facilities, drones, air defense systems, radars and one helicopter, according to a joint statement.

“These precision strikes are intended to disrupt and degrade the capabilities that the Houthis use to threaten global trade, naval vessels, and the lives of innocent mariners in one of the world’s most critical waterways,” the statement read.