The findings "close the door" on Egyptian suggestions that a bomb caused the Paris-Cairo flight to crash into the Mediterranean on 19 May 2016 with 66 people on board, including 15 French nationals and 40 Egyptians, the source told the AFP news agency.
Gendarmes have examined samples taken from the bodies of eight French victims repatriated in January and found no powder from explosives, AFP reports.
In December last year the Egyptian investigative committee claimed to have found traces of explosives.
But French investigators' were sceptical, especially since no organisation has claimed responsibility for the blast.
They believe the most probable cause was the combustion of a tablet in the cockpit but have been unable to examine debris that might prove or disprove the hypotheses because "the Egyptians have not showed a great willingness to collaborate", the source said.