The U.S. Embassy in Saudi Arabia issued an urgent security alert on Sunday warning of escalating regional threats from Yemens Houthis, urging American citizens to exercise extreme caution as King Khalid International Airport in Riyadh partially reopened following a wave of ballistic missile and drone attacks. The US Embassy in Saudi Arabia warned on Sunday of escalating security threats from Yemen's Houthis as the capital Riyadh's main airport partially reopened following repeated.