That possibility prompted British authorities to delay flights from Sharm el-Sheikh, Egypt, the city from which the Russian flight departed, to the United Kingdon, the British Prime Minister’s office said.

The announcement comes in the wake of Saturday’s crash that broke apart in midair, an incident that is under heavy scrutiny by investigators.

“While the investigation is still ongoing we cannot say categorically why the Russian jet crashed,” the Prime Minister’s office said. “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.”

The delay of “flights due to leave Sharm for the UK this evening” is precautionary, to allow UK aviation experts to assess security arrangements at Sharm el-Sheikh’s airport, Cameron’s office said in its statement.