Investigations into the Russian plane crash that left all 224 people on board dead are underway in Cairo.

They come amid confusion about what caused the A-321 airbus to break apart mid air.

International correspondent Annabell Van Den Berghe said given what they now know, Russian and Egyptian authorities are having to reconsider the options.

"We thought that it happened on the ground..but now we know that this was not the cause, that basically it was believed to be in two parts - while it was still in the air."

She said while initially it was thought to be a technical fault, investigators are beginning to consider a deliberate attack as another potential cause.

A Russian official said the disintegration happened in the air and fragments are strewn over a large area.

The same official said it's too early to draw conclusions about what caused the crash which killed all 224 people travelling from an Egyptian resort to Saint-Petersburg.

The black boxes are being analysed and Russian transport officials have ordered the airline to check all its other Airbus 321 planes as part of an urgent safety review.

A group affiliated to Islamic State claimed it downed the plane, but Egyptian Prime Minister Sharif Ismail said the group wasn't technically capable of shooting down an airliner flying at 30,000 feet.