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.
Airport security around the world will have to be tightened if it is confirmed the Russian plane crash was caused by a bomb, the Foreign Secretary has warned.
Philip Hammond said there would have to be a major re-think of airport security in countries where so-called Islamic State (IS) is active if it turned out they were behind the attack.
He said tourists may face extra delays checking in at airports if security needs to be increased.
Speaking to BBC1's Andrew Marr Show, he said: "If this turns out to be a device planted by an IS operative, or by somebody inspired by IS, then clearly we will have to look again at the level of security we expect to see in airports in areas where IS is active."
Egyptian officials investigating the crash which killed 224 people say they are now "90% sure" it was a bomb which brought the plane down.
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.