An external phone charger appears to have caused a fire which forced a flight from New York to London to make an emergency landing in Boston.
Massachusetts State Police's Explosive Ordnance Disposal Unit examined the Airbus A330 after it landed and found a device between the cushions of a seat which had ignited.
"Preliminary investigation suggests it is a battery pack consistent in appearance with an external phone charger," a police spokesman said.
Virgin Atlantic Flight 138 left John F Kennedy airport at around 8pm (1am BST) on Thursday bound for Heathrow where it was due to arrive at around 7.20am.
Information from Flightaware showed the aircraft began to descend around 25 minutes after takeoff, landing at Boston Logan International at 8.50pm (1.50am BST).
All 217 passengers and crew were safely evacuated.
One passenger refused treatment for a smoke-related complaint, police said.
Virgin Atlantic said it is "currently investigating" what led to smoke appearing in the cabin of Flight 138.
"The safety and security of our customers and crew is always our top priority and we are currently investigating to fully understand the circumstances," a company spokeswoman said.
"We'd like to thank our customers for their patience as we work with them to provide local accommodation or to rebook alternative flights to their final destination."