By AFP | Posted by TOE The United States warned Saturday that hostilities between Saudi Arabia and Iran-backed Houthis could “escalate rapidly” after a missile attack targeted Riyadh for the first time since the Yemen conflict resumed. US President Donald Trump cut short a weekend at Camp David, a secluded presidential complex in rural Maryland, to return unexpectedly to the White House on Saturday. The White House gave no explanation for the early return, which comes as a new threshold was cros