The Russian plane that crashed in Egypt at the weekend "may well have been brought down by an explosive device", Downing Street has said. All flights between the UK and Sharm el-Sheikh have been suspended on Wednesday evening as UK experts assess security at the Egyptian airport.
Number 10 said flights had been delayed as a "precautionary measure" after "more information has come to light". Russian Airbus 321 crashed on Saturday, killing all 224 people on board.
The Metrojet flight bound for St Petersburg from Sharm el-Sheikh came down in Egypt's Sinai desert. A senior UK government source told the BBC that fresh intelligence to emerge during the last 24 hours pointed towards a bomb causing the crash.
Egypt's foreign minister, Sameh Shoukry, said he was very disappointed by the decision to suspend flights, accusing the UK government of making "a premature and unwarranted statement" on the crash.
Almost from the moment it was confirmed that Metrojet Flight 9268 had crashed into the Sinai desert, British counter-terrorism officials have been looking at what could have brought it down and what the implications were for the safety of Britons abroad.
The analysis has brought together aviation and anti-terrorism experts. The Egyptian authorities were quick to dismiss claims by so-called Islamic State that they brought the plane down.
However, British officials now say "new intelligence" has come to light pointing increasingly towards the possibility of terrorism. They have not revealed what that new intelligence is, or where it came from. But the government says it cannot take a risk with the safety of so many Britons flying to and from such a popular resort.
What we know about crash
Four theories on Sinai plane crash. Downing Street said aviation experts had travelled to Egypt assess security arrangements at Sharm el-Sheikh airport.
Their findings were considered in a one-hour meeting of the government's Cobra emergency committee, chaired by Prime Minister David Cameron.
A further government statement is expected later tonight. The Irish Aviation Authority said it has directed Irish airlines not to fly to or from the area until further notice.
Transport Secretary Patrick McLoughlin said the delays would allow UK experts time to make sure "the right security measures are in place" at the airport.
"We cannot categorically say why the Russia jet crashed but we have become concerned that the plane may well have been brought down as a result of an explosive device," he said.
Egypt's President Sisi is currently in the UK and is due to meet Mr Cameron on Thursday. They spoke on Tuesday, before Downing Street released its statement.
The BBC's Christian Fraser said there are around 2,000 British holidaymakers currently in Sharm el-Sheikh. Thomas Cook confirmed it currently has 1,700 holidaymakers in the Egyptian resort, adding that it would "continue to monitor the situation".
Easyjet said it had delayed two UK-bound flights from the resort - one to Gatwick and one to Luton airport - this evening. "We are doing all possible to keep passengers informed," a spokesman added.
Thomson has suspended its flights to and from the resort. Meanwhile, a spokesman for British Airways, which is due to fly to Sharm el-Sheikh on Thursday, said: "Things are moving fast and we are waiting for the government to update later in the evening."
The government said it recognised that the latest advice "may cause concern" for Britons already in the holiday resort and for those planning to travel, saying people should contact their airline or tour operators.
Extra consular staff have been deployed to the airport, it added. Foreign Office travel advice for passengers travelling to Egypt has not changed.
British holidaymaker Craig Peacock, who has been in Egypt for nine days, said finding out he may not be able to return home is "not the greatest news". But, he said, postponing flights was "the right thing", adding: "We don't want a repeat of what happened last week".
Another tourist, Sarah Cotterill, from Portsmouth, is at the airport waiting for a flight home, alongside several hundred other travellers. She said there has been little information and airport staff have "no idea" how long they will be waiting.
Simon Calder, travel editor at the Independent, said "hundreds" of holidaymakers are due to fly back on Thursday or Friday, saying airlines might fly empty planes to Egypt in order to bring people home. Sharm el-Sheikh is a popular holiday destination for Britons.