The U.S. State Department called on American citizens to “exercise increased caution” while traveling to Saudi Arabia, Report informs citing CNBC.

U.S. Mission personnel and their families are not permitted to use the airport in Abha without Chief of Mission approval, the note added. Abha airport has been frequently attacked by drones and missiles launched from Yemen, where a Saudi-led coalition has been battling the Houthi group.

Saudi Arabia’s largest oil plants were targeted in drone and missile attacks early Saturday morning that knocked out more than half of the kingdom’s global daily exports. Authorities told the public that the ensuing fires were contained and there were no casualties.