A Houthi drone boat packed with explosives detonated in the Red Sea on Thursday, but failed to cause any damage or casualties, the US Navy said, as the Iran-backed militias in Yemen continued their attacks in defiance of international calls to stop. The latest attack came one day after 12 countries including the US Britain and Japan issued a joint statement cautioning the Houthis of unspecified "consequences" unless it halts its attacks, in what one US official on Wednesday suggested was a final warning.