The State Department issued a caution warning to Americans in the Middle East on Saturday night after Houthi rebels in Yemen launched a ballistic missile at an airport in Riyadh, Saudi Arabia’s capital.

“Due to tensions in the Middle East, the security environment remains complex with the potential for unforeseen escalation,” the announcement said. “Americans currently in the Middle East should exercise heightened vigilance and be aware of potential flight cancellations, airspace closures, and travel disruptions.”