The United States and Britain have issued safety alerts to their citizens after Houthi rebels struck two major Saudi Arabian airports with missiles over the weekend. The targets were the air terminals in Riyadh, the Saudi capital, and in Dammam, cities that anchor the kingdom's main population centres. The attacks left more than 300 people injured and 13 dead, a casualty count high enough to alarm governments whose nationals pass through those airports daily. In response, Washington and London warned their citizens to exercise caution and to review any travel plans involving Saudi Arabia. Houthi fire on Saudi territory is not new, but a direct assault on civilian airport infrastructure marks an escalation in both method and impact. Airports are sensitive targets because a strike there scrambles international flight schedules and unsettles the risk assessments of airlines around the world. The rebels have framed their campaign as part of a broader confrontation with Saudi Arabia and its partners in the region. With the death toll now at 13, questions are turning to how Saudi air defences allowed the missiles through.