Britain said on Wednesday that the Russian plane that crashed in Egypt this week after taking off from the resort of Sharm al-Sheikh might have been brought down by an explosive device.
"While the investigation is still ongoing we cannot say categorically why the Russian jet crashed," Prime Minister David Cameron's office said in a statement.
"But as more information has come to light we have become concerned that the plane may well have been brought down by an explosive device," it added.
As a precautionary measure, the government has decided that flights due to leave Sharm for Britain on Wednesday evening will be delayed to allow time for a team of UK aviation experts, currently travelling to Sharm, to make an assessment of the security arrangements in place at the airport.