Flights from Sharm el-Sheikh to the UK were suspended tonight amid fears that a Russian plane was brought down by a bomb, Downing Street has announced.
The "precautionary" move is to allow time for a specialist British team to assess security arrangements in the Egyptian resort, where there are believed to be as many as 20,000 Britons at present.
David Cameron summoned senior ministers and security officials for a meeting of the Government's emergency Cobra committee to discuss the latest developments.
He will hold face-to-face talks tomorrow with Egyptian president Abdel Fatah al-Sisi, who was due to arrive in the UK this evening for a controversial scheduled visit to the UK.
The leaders spoke by telephone about the crash last night.
A Number 10 spokeswoman said: "While the investigation is still ongoing we cannot say categorically why the Russian jet crashed.
"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.
"In light of this, and as a precautionary measure, we have decided that flights due to leave Sharm for the UK this evening will be delayed.
"That will 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 and to identify whether any further action is required. We expect this assessment to be completed tonight."
All 224 people on board were killed when the Metrojet flight bound for St Petersburg from Sharm came down in the Sinai desert on Saturday.
The nature of the crash and the lack of an SOS call have fuelled speculation that it was caused by a bomb or missile.
Extra consular staff have been deployed to the airport but there has as yet been no change in official travel advice - which excludes Sharm and other Red Sea resorts from a caution against "all but essential" visits to other nearby parts of Egypt.
Thomson said it had temporarily suspended flights to and from the Egyptian resort and British Airways said it was "liaising closely with the Government and awaiting further information".
The visit of Mr al-Sisi has drawn strong criticism from human rights campaigners, with Labour leader Jeremy Corbyn accusing Mr Cameron of showing "contempt" for democracy by "rolling out the red carpet".
Downing Street has insisted that "no issues are off the table" during bilateral discussions with the former head of Egypt's armed forces, who overthrew Islamist president Mohammed Morsi.