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.
US President Barack Obama says there is a "possibility" that the crash of a Russian passenger plane in Egypt was caused by a bomb on board the plane.
"I think there's a possibility that there was a bomb on board. And we're taking that very seriously," Obama said in an interview with KIRO/CBS News Radio.
"We're going to spend a lot of time just making sure our own investigators and own intelligence community find out what's going on before we make any definitive pronouncements. But it's certainly possible that there was a bomb on board," he said.
It follows comments made by David Cameron earlier today that the jet "was more likely than not" brought down by a bomb.
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.