A US military satellite detected a heat flash over the Sinai at the time a Russian airliner crashed, killing all 224 people aboard, US media reported.

The Airbus A321 plunged to the ground Saturday 23 minutes after taking off from the Red Sea resort of Sharm-el-Sheikh on a flight to St Petersburg.

Experts have said the fact that debris and bodies were strewn over a large area were signs the plane broke up in mid-air, a rare but not unprecedented event.

A US intelligence analysis has ruled out a missile strike, as claimed by a militant group affiliated with Islamic State, CNN reported.

But US officials told CNN and other US television networks that a military satellite detected a heat flash at the time of the crash, which points to a catastrophic event during flight, possibly the result of a bomb explosion although analysts were considering a range of possible causes.

Among other possibilities cited by the CNN report were the explosion of a malfunctioning engine, a fire caused by a structural problem on the plane or wreckage hitting the ground.

Investigators on Tuesday began examining the plane's two black boxes, one of which recorded on-board conversations and the other flight data, Egyptian civil aviation officials said.

Egypt's President Abdel Fattah al-Sisi, who has dismissed the missile strike claim as IS "propaganda," said it would take time to establish the cause of the crash.