The UK's foreign secretary Philip Hammond has said there is a "significant possibility" that Isis was responsible for destroying the Metrojet A231 flight 7K9268, killing all 224 people on board.
Hammond was speaking ahead of a second Cobra meeting, which will be chaired by David Cameron later today, after the Prime Minister suspended all flights out of Sharm el-Sheikh yesterday.
That decision was taken after it emerged that the US had evidence of a "heat flare" suggesting the plane had been blown up mid-flight.
Hammond told Good Morning Britain: "We have formed a view, looking at the whole picture of information that’s available to us - that’s information that’s already in the public domain, peripheral information, intelligence information and building a picture - we formed a judgement that there is a significant possibility that the Russian aircraft was brought down by an explosive device on board.
"Once we’ve formed that judgement we have to act on it - we have to act to ensure that British nationals travelling back from Sharm el-Sheikh are safe."
During an interview with the Today Programme on Radio 4, the foreign secretary went on to confirm that all 20,000 Brits currently in Sharm el-Sheikh would be brought home "regardless of cost", adding the operation may need "additional personnel".
Hammond said he expected other nations to also deploy short-term measures for their citizens' safety when leaving the popular holiday destination.
The move is already taking its toll on the region, with Hammond admitting that 3,500 tourists were due to fly out today alone. He also revealed that the ban was imposed prior to the UK advising Egypt of the move.