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.
It is "increasingly likely" the Russian airliner which crashed in Egypt was brought down by a bomb, the Prime Minister has said.
David Cameron said he could not be certain that the crash was caused by a bomb, but it was a "strong possibility".
Mr Cameron said it could "take some time" to start flying UK tourists back from Sharm el-Sheikh as it was vital to ensure their safety.
He said there were some "relatively simple and straightforward" measures required at the airport to reassure the Government about security there.
Mr Cameron expressed sympathy with British holidaymakers caught up in the disruption, as well as Egyptian concerns about the implications for tourism in the area.
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.