Source from Egypt:
The cause of a Russian plane crash in Egypt is looking more like an explosion but it is not clear whether it was linked to a fuel or engine trouble or a bomb, an Egyptian source close to the investigation said on Wednesday.
(...) "It is believed to be an explosion but what kind is not clear. There is an examination of the sand at the crash site to try and determine if it was a bomb," the source, who is close to the team investigating the black boxes, told Reuters.
"There are forensic investigations under way at the crash site. That will help determine the cause, to see if traces of explosives are found."
Source from Russia:
An investigation into the crash of a Russian plane in Egypt last Saturday is looking into the possibility of an object stowed on board causing the disaster, a Russian aviation source said on Wednesday.
"There are two versions now under consideration: something stowed inside (the plane) and a technical fault. But the airplane could not just break apart in the air – there should be some action. A rocket is unlikely as there are no signs of that," the source said.