A flight to Washington, D.C., returned to Nigeria after “unexpected aircraft movement” caused injuries, United Airlines said. A statement from United emailed to The Hill on Monday said that one of its flights headed for Washington,

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.”

A United Airlines flight bound for Washington Dulles International Airport had to turn back to Nigeria Friday after a technical issue with the plane injured multiple people, according to the airline.

Six people, four passengers and two crewmembers, were injured on a United Airlines flight Friday from Lagos, Nigeria, to Washington Dulles International Airport in Virginia, according to the airline.

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.

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.