A D.C.-bound United Airlines Flight had to make an emergency landing in Nigeria on Friday after passengers and crew members were injured by an ‘in-flight jolt,’ that caused food trays, drinks, and passengers' belongings to fly throughout the cabin.

It is unclear what caused the jolt; United Airlines has said the cause was not severe turbulence, and that it is “working with aviation authorities in the US and Nigeria to understand the cause.”

United Airlines said it was cooperating with U.S. and Nigerian investigators to determine what exactly happened on the flight.