Houthi militants struck a Barbados-flagged, Liberian-owned commercial vessel off the coast of Yemen on Wednesday, killing three civilian mariners, U.S. officials said — the first known fatalities since the Houthis began targeting ships in what they describe as a response to Israel’s actions in Gaza. On Wednesday evening local time, the United States conducted self-defense strikes against two unmanned aerial vehicles that threatened U.S. Navy and maritime vessels in the area.