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.
Intercepted intelligence "chatter" supports the theory that a bomb took down a Russian passenger jet, killing all 224 people on board, US officials have said.
However, officials in both the US and Europe have warned that conclusive forensic evidence of a bomb blast was still lacking. A technical failure has not been ruled out, they added.
One source told Reuters news agency that there was conflicting intelligence reporting over where the "bomb" - if indeed there was one - may have been placed on the plane.
It comes after ITV News learned that a specific piece of 'signals intelligence' - such as an eavesdropped conversation - picked up at the GCHQ listening station convinced Prime Minister David Cameron that a bomb may be to blame.
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.