The U.S. Embassy in Riyadh has issued an urgent security alert warning of an imminent missile and UAV attack threat over Dhahran.
U.S. citizens are being instructed not to approach the U.S. Consulate and to shelter in place immediately.
Officials advise taking cover on the lowest level of a building, away from windows and exterior walls, and to remain indoors.
The embassy warns that even intercepted missiles or drones could pose a serious danger from falling debris.
Consulate personnel are currently sheltering in place as authorities monitor the situation for further developments.
On Monday, the massive Ras Tanura refinery on Saudi Arabia's Gulf coast went into partial shutdown after a strike by drones.
The complex run by the Saudi state oil giant Aramco is home to one of the largest refineries in the entire Middle East and a cornerstone of the kingdom's energy sector.
Saudi Arabia is the world's biggest oil exporter, with most of its oil fields and petroleum infrastructure located along its eastern coast, across the Gulf from Iran.