Egypt plane crash investigators "90% sure" the explosion heard on the black box recording of the Russian flight was a bomb, a member of the investigation team told Reuters.
A memorial service for the 224 victims of the crash was be held in St Petersburg today.
Egypt's president Abdel Fattah el-Sisi has said the investigation into the cause of the Russian plane crash "could take months."
"This is a complicated matter and requires advanced technologies and broad investigations that could take months," he said in a televised speech.
Meanwhile Egyptian analysts have begun examining the contents of two black boxes recovered from the airliner but say it could take days to retrieve the data.
Russian investigators have said they will consider all possible causes of will consider all possible scenarios as to why the jet crashed in the Sinai region on Saturday, a spokesman for Russia's Investigative Committee said in a statement.
Investigators now have the technical documentation for the plane for the whole period of its use and had questioned employees responsible for safety checks at the airport as well as well as crew on a recent Kogalymavia flight.
Airline Kogalymavia, who owned the doomed jet said "we can't doubt the professionalism of the pilot and crew of the crashed plane in Egypt," adding "all our planes are serviced regularly and tested before flights."
Terrorists would be able to bypass the wand-like devices being used to scan luggage in Sharm el-Sheikh, an expert has claimed.
Intelligence showed a "significant possibility" that the crashed Russian passenger jet was brought down by an explosion, ITV News was told.
As flights from Sharm el-Sheikh to the UK are delayed over bomb fears, we review what is known about the Egyptian plane crash tragedy.