Russian officials do believe the Metrojet plane which crashed in the Sinai was brought down by a bomb, US intelligence suggests.
Moscow had previously rejected the West's claims that an explosion occurred on the Airbus A321, killing all 224 people on board.
However, Reuters has reported that Russian officials monitored by the US now believe this assessment is correct.
At the weekend, investigators said they were "90% sure" that a noise heard on the airliner's black box was caused by a bomb - and a "spectral analysis" on the cockpit voice recorder is taking place.
A group affiliated to Islamic State has claimed responsibility for bringing down the plane but has not provided any evidence to confirm it was behind the attack.
The downing of the passenger jet has renewed concerns about security at Sharm el Sheikh International Airport - and the resumption of flights between Britain and the Egyptian resort have been hit by further delays.
EasyJet, Monarch, Thomson Airways and Thomas Cook have extended the period for cancelled outbound flights up to and including 25 November.
British Airways said it will not operate flights up to 23 November.
