RUSSIAN media reports say unusual sounds have been heard from cockpit recordings at the moment a Russian passenger plane crashed in Egypt’s Sinai Peninsula at the weekend.

The news came after revelations by United States (U.S.) broadcasters that satellite images had detected a heat flash at the time of the crash that killed all 224 people on board the Airbus A-321.

“Before the moment of the disappearance of the aircraft from radar screens, sounds are recorded which are not characteristic of a normal flight,” Interfax quoted an unnamed security source in Cairo as saying.

A team of investigators led by Egypt and aided by experts from Russia, Airbus and Ireland visited the crash site on Tuesday as they try to find out the cause of the deadly crash.

Once investigations at the site finish, investigators are expected to focus on analysing the black box recorders, which are reportedly in good condition and could bring officials closer to finding out how the jet came crashing down.

On Tuesday, a U.S. official said that the U.S. intelligence community believed that it could have been some kind of explosion on the plane itself, either a fuel tank or a bomb.