Sisi is quite right. It is far too early to know what caused the Russian Metrojet airliner to fall out of the sky on Saturday just 23 minutes after it left the Sharm El-Sheikh resort en route for St Petersburg with 224 passengers and crew on board. The two black box flight recorders are only now being examined, yet the Metrojet management have felt themselves able to deny that there had been any problem with the aircraft. There must, said the carrier's operations' manager, have been some external cause for the crash. The Putin Kremlin, like Sisi, is counseling against rushing to conclusions. Terrorists linked to Daesh (the self-proclaimed IS) have claimed that they were responsible for downing the airliner. They did not say how this had been achieved. Security analysts have opined that it is not thought the terrorists operating in the Sinai have rockets able to reach aircraft at some 10,000 meters. If it was a terror attack, it is more likely that it was an explosive device that was somehow taken or put on board the plane. Only a thorough examination of the wreckage together with evidence from the flight recorders will enable investigators to piece together - quite literally in the case of the remains of the airframe - exactly what happened. It will not have been lost on more thoughtful Russians that it took international investigators fully 14 months to issue a definitive report into the destruction in mid-air of Malaysian Airlines Flight MH17 over Ukraine in July 2014. That investigation concluded that, without doubt, the airliner had been hit by a Russian-built Buk missile. Though there is strong evidence to suggest that the missile was fired from the pro-Moscow rebel territory around Donetsk, it was not part of the enquiry's brief to apportion blame. The general belief is that the Buk was targeting a Ukrainian transport plane being used for surveillance. The notion that the Metrojet destruction was an act of terrorism is strengthened by Russia's military intervention in Syria to save the Assad regime. Yet although Putin's warplanes have targeted Daesh positions, most recently Monday's airstrike on Palmyra, the greatest part of Moscow's assault has been focused on the Free Syrian Army, who themselves are struggling against Daesh fanatics. Sisi has described the terrorist claim that they destroyed the Russian aircraft, as "propaganda". This, however, is to overlook the reality that propaganda, at which Daesh has proved itself hideously adept, is not necessarily a lie. If a bomb was smuggled on board the doomed plane, there are serious questions to be answered by Egyptian security. With tourist numbers to its magnificent archaeological heritage along the Nile badly hit by terrorist violence, the purely vacation resorts surrounding Sharm El-Sheikh on the tip of the Sinai peninsula have been the one remaining source of tourist dollars. This is a tragedy that is still very far from being understood. It is obvious why the Russian carrier should be seeking to deny any responsibility - obvious but not wise. It seems equally clear that Daesh's claims of responsibility, even if they are opportunist nonsense, should not be ignored. The brutal truth is that even if they did not destroy this aircraft, they would have done so if they could. The lesson then is that everyone concerned, including other international airlines servicing the Egyptian Sinai resorts must redouble their security.