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.

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

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.”

The authorities in Nigeria said that the United Airlines plane had to return to Lagos, Nigeria, after the episode. Six people were treated at a hospital, officials said.

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.

A United Airlines flight had to make an emergency landing in Lagos, Nigeria due to a midair incident causing loss of pressure and sharp descents.

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

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

A United Airlines flight between Nigeria and the US experienced sudden, unexpected movement inflight, injuring 38 people

After diverting, United Airlines Flight UA613 landed safely back in Nigeria. Four passengers and two flight attendants were taken to hospital with injuries but have been discharged, United Airlines said in a statement. The Federal Airports Authority of Nigeria (FAAN) said an additional 27 passengers and five crew members sustained minor injuries.