There is no evidence of a direct link between the Boeing 787 Dreamliner's batteries and the fire at Heathrow Airport on Friday, investigators said.
The fire on the parked Ethiopian Airlines plane closed the London airport's runways for 90 minutes.
At the start of the year, all 50 Dreamliners in service worldwide were grounded after two separate incidents concerning batteries.
But the investigators found the fire damage was not near the batteries.
The aircraft is currently in a hangar at Heathrow while the investigation is carried out.Rear fuselage
The UK's Air Accidents Investigation Branch said the initial investigation was likely to take several days.
It said it had found "extensive heat damage in the upper portion of the rear fuselage, a complex part of the aircraft".
"However, it is clear that this heat damage is remote from the area in which the aircraft main and APU (Auxiliary Power Unit) batteries are located and at this stage there is no evidence of a direct causal relationship."
The AAIB will lead the investigation, with involvement from Boeing, the US Federal Aviation Administration, the US-based National Transportation Safety Board, the Civil Aviation Authority of Ethiopia, Ethiopian Airlines, the European Aviation Safety Agency and the UK Civil Aviation Authority.
Ethiopian Airlines has said it will continue operating its fleet of Dreamliners.
It said the plane had been parked for eight hours before smoke was spotted and the incident was "not related to flight safety".
There were no passengers aboard the plane, named the Queen of Sheba, when it caught fire.
When it was spotted, fire-retardant foam was sprayed at the airliner. The area on top of the fuselage in front of the tail appeared to be scorched.Emergency landing
The Dreamliner was marketed as a quiet, fuel-efficient aircraft carrying between 201 and 290 passengers on medium-range routes.
It was due to enter passenger service in 2008 but it was October 2011 before the first commercial flight was operated.
On 7 January, a battery overheated and started a fire on a Japan Airlines 787 at Boston's Logan International Airport.
Nine days later, an All Nippon Airways 787 had to make an emergency landing in Japan after a battery started to give off smoke.
In response, all 50 Dreamliners in service at the time were grounded. Boeing modified the jets with new batteries and flights resumed in April.