Egyptian officials said Wednesday that evidence found in the wreckage of EgyptAir Flight 804, which crashed last month, and data retrieved from one of its "black boxes" show there may have been a fire on the plane.

The flight data recorder contains information consistent with fault warnings transmitted by the Airbus Group SE A320 that pointed to smoke in one of the lavatories and the avionics bay located under the cabin floor and behind the cockpit, where key electronics are housed, Egyptian crash investigators said.

Wreckage recovered from the plane that crashed May 19, killing all 66 people aboard, also showed signs of high temperature damage and soot, they said.

By itself, the latest information doesn't indicate what may have touched off a fire or specifically which onboard systems it could have affected, according to independent air-safety experts monitoring the probe.

But the findings offer the clearest evidence yet that a handful of automated messages transmitted by the Airbus A320 pointing to smoke or fire in the nose of the plane weren't erroneous.

The latest details also strongly suggest the pilots were dealing with a combination of smoke and serious electrical malfunctions -- potentially involving various systems -- before the jetliner started a sharp turn, continued a more shallow turn in the opposite direction and then descended fairly rapidly.

The latest evidence points to a nearly simultaneous shut-off of both the plane's flight-data recorder and an alerting system designed to transmit malfunction messages to the ground. Those twin events can't be intentionally commanded by pilots, according to safety experts, and aren't part of any authorized emergency procedures to respond to fire or smoke.

The upshot, according to these experts, is that the pilots may have been struggling to cope with a significant electrical malfunction, or possibly a cascading series of malfunctions, while still at cruising altitude.

Widespread electrical problems, these experts said, most likely would have made the aircraft harder to fly by shutting off certain computerized flight-control aids. Under such circumstances, the cockpit crew would have confronted the loss of certain built-in safeguards intended to prevent aerodynamic stalls or other extreme maneuvers.

Accident investigators still haven't determined why the plane, flying from Paris to Cairo, crashed.

Investigators said they are still working to repair the cockpit voice recorder, which was taken to France. French air-accident investigators are aiding the Egyptian-led probe. Once the device is repaired, it will be returned to Cairo for analysis. The cockpit voice recorder could yield information about how pilots reacted to the apparent smoke messages.

The flight-data recorder stores technical details from the previous 25 hours of an aircraft's operations. The cockpit voice recorder retains the last two hours of crew conversation.

Investigators also said information on the flight data recorder, which was returned to Egypt on Tuesday after being repaired in France, covers the flight until the recording suddenly stopped with the plane at an altitude of 37,000 feet.

Egyptian officials said they would try to determine the source of the apparent high-temperature damage.

Write to Andy Pasztor at andy.pasztor@wsj.com and Robert Wall at robert.wall@wsj.com