The U.S. National Transportation Safety Board said on Monday it is investigating a United Airlines flight on Friday from Lagos, Nigeria to Washington D.C., in which a sudden aircraft movement led to injuries of passengers and cabin crew.

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.

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 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.

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 flight was diverted shortly after take-off due to a mid-air jolt which has injured several people - we'll be bringing you the latest updates, pictures and video on this breaking story

A United Airlines flight to Washington, DC, was forced to make an emergency landing after the Boeing plane abruptly plunged in midair, hurting nearly 40 people onboard, including six hospitalized with serious injuries,

Nearly 40 people were injured, with six seriously injured, when a Boeing aircraft operated by United Airlines suddenly plunged in mid-air, forcing the fight to make an emergency landing. According to CNN,

A United Airlines flight from Nigeria was forced to make an emergency landing after six people were injured following an unexpected mid-air jolt.