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.

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.”

Nearly 40 people were injured when a Boeing 787-800 plane suddenly lost altitude during a United Airlines flight from Lagos, Nigeria, to Washington, D.C., early Friday, officials said.

Six were injured on a United Airlines flight from Lagos to Washington after the plane had a technical issue that caused an "unexpected movement."

The United States National Transportation Safety Board (NSTB) has said it is investigating a United Airlines flight from Lagos to Washington

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

The plane headed back to Nigeria after experiencing "unexpected movement" mid-flight on Friday, Jan. 24, according to multiple reports

Six people were injured on a flight from Nigeria to Virginia. The airline also saw a series technical issues in March.

Six people were taken to hospital with injuries but have been discharged, United Airlines said.

The same United Airlines aircraft had a similar issue earlier this week, with a rapid altitude drop prompting a diversion.

In an update, Nigerian officials said an additional 27 passengers and 5 crew members suffered minor injuries in the incident. In all, 38 were hurt.