The United States warned that fighting between Saudi Arabia and the Iran-backed Houthis could “escalate rapidly” after a missile attack targeted Riyadh for the first time since the Yemen conflict resumed.

U.S. President Donald Trump cut short a weekend at Camp David, a secluded presidential complex in rural Maryland, to return unexpectedly to the White House.

The White House gave no explanation for the early return, which comes as a new threshold was crossed in the conflict between Saudi Arabia and the Houthis, who control a large part of Yemen and are fighting government forces backed by a coalition led by Riyadh.