Islamic State bomb 'may have brought down Russian plane', US and European officials say

A bomb planted by IS or an affiliate group was the most likely cause of the Russian jet crash in Egypt, US and European officials have said.

An American official told NBC News that investigators were looking at the possibility that an explosive device was planted aboard the plane by ground crews, baggage handlers or other ground staff at the Sharm el-Sheikh airport before takeoff.

European security sources also told Reuters there was evidence IS was responsible for the tragedy.

Earlier, officials said there was not thought to have been anyone on the flight with suspected ties to any terrorist group.

One US official said the bomb theory was not the official conclusion of the intelligence community, but it was a strong possibility.

"There is a definite feeling it was an explosive device planted in luggage or somewhere on the plane," the official told CNN.

The Airbus A321, operated by Russian airline Metrojet as flight KGL9268, was carrying holidaymakers from the Red Sea resort of Sharm el-Sheikh to St Petersburg.

It crashed with 224 people on board in Egypt's Sinai Peninsula on Saturday after breaking up in mid-air.