An analysis of black boxes from the Russian airliner that crashed in Egypt on Saturday point to a bomb attack, sources close to the probe said Friday, as Moscow halted flights to the country.

The flight data and voice recorders showed that "everything was normal" until both failed at 24 minutes after takeoff, pointing to "a very sudden explosive decompression," one source.

The data "strongly favours" the theory that a bomb on board had brought down the plane, he added.

Another source said the plane had gone down suddenly and violently.

The black boxes contained the sound of an explosion during the flight, an investigator told France 2 Sunday. According to him, this explosion cannot be the result of an engine problem, which would eliminate the hypothesis of an accident.