If you read through the full thread on PPRuNe (which is a forum with many thousands of pilots on) it seems almost certain that the aircraft broke apart in mid air. This could be caused by a missile strike, however it could also be caused by some catastrophic failure... This airframe did suffer a tail strike back in 2004, in Cairo ironically, which could be a point to look at, if this has caused some fatigue that has eventually failed.
It will be interesting to see what the investigators find