A United Airlines flight from Africa to Washington D.C. had to turn around on Thursday after a "technical issue" caused "unexpected aircraft movement," the airline said.

A United Airlines jet was forced to make an emergency landing after plummeting mid-air following take-off. At least six people were injured after the plane jolted during the flight from Nigeria on Friday. The flight, which was heading from Lagos to Washington DC, had 245 passengers and 11 crew on board at the time.

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.”