Investigations are on to find out the causes leading up to the crash of Russian Metrojet Flight 9268 carrying 224 people on board, mostly Russians, which went down over the Sinai peninsula on the way to St. Petersburg from Sharm el-Sheikh in Egypt.
A US military satellite detected a midair heat flash in the area before Airbus A-321-200 crashed, according to CNN.
An Islamic State affiliated terrorist organization took responsibility for downing the passenger plane with a missile, "in response to Russian airstrikes that killed hundreds of Muslims on Syrian land". But the claim was debunked by Egyptian and Russian officials, because the terrorists do not have a surface-to-air missile to fire planes thousands of meters above ground. The Russian plane was flying at an altitude of 10,000 m (32,808 ft).
Also a missile attack was reportedly ruled out by the military satellite, as the heat flash did not leave a trail which would have been left by a rocket engine.
However, the heat flash may not be from the crash at all, as militant warfare is common to the Sinai region, which are recorded as heat activities on satellite imagery, a Pentagon official told ABC News.
President Abdul Fattah al-Sisi said that the area above Sinai desert is safe and under the control of the Egyptian government.
"When there is propaganda that it crashed because of ISIS, this is one way to damage the stability and security of Egypt and the image of Egypt. Believe me, the situation in Sinai - especially in this limited area - is under our full control," he told the BBC.
The US intelligence team studying the circumstances surrounding the crash said that a fuel tank, malfunctioning engine, or bomb could have been possible causes of the explosion.
But the Russian airliner insisted that the plane crashed owing to an external event.
"The only explainable cause is physical impact on the aircraft. There is no combination of system failures that could have broken the plane apart in the air." said Alexander Smirnov, deputy general director of Metrojet.
The Russian aviation authority head, Aleksand Neradko said the company's assertion was "premature and not based on real facts."
"There is much work to be done to study the debris of the aircraft and the data of the flight recorders. The debris is indeed spread over a large area indicating that the plane fell apart at a high altitude. But speculating on the cause is premature," he told Rossiya 24 news channel.
The cockpit recordings from the recovered black boxes indicate unusual activity and sounds before the plane crashed, but these were not distress calls.
The pilots had exchanged routine conversations with the air traffic controllers, just four minutes before the plane went down. The Moscow-based Interfax news agency quoted an anonymous source saying, "sounds uncharacteristic of routine flight were recorded preceding the moment that the aircraft disappeared from radar screens."
Smirnov said that the plane slowed to 186 mph and fell down about 1524 m (5000 ft) a minute before it crashed. An air tracking service Flightradar24 also said that the plane underwent steep change in altitude and sudden decrease in ground speed before disappearing from the radar.
Twelve large pieces of the plane were recovered from the crash site.
The airbus was over 17 years old, and Metrojet started using it since 2012. The plane had operated about 21,000 flights and accumulated over 56,000 flight hours.
