President Joe Biden said on Saturday the United States had delivered a private message to Iran about Iran-backed Houthis responsible for attacking commercial shipping in the Red Sea. "We delivered it privately and we're confident we're well-prepared," Biden told reporters at the White House before departing to the Camp David presidential retreat for the weekend. The Houthi movement threatened a "strong and effective response" after the United States carried out another strike in Yemen overnight, further ratcheting up tensions as Washington vows to protect shipping from attacks by the Iran-aligned group.