In his first public comments on the crash, President Vladimir Putin said it was a "dreadful tragedy" and called for a "fully objective" investigation.
"Without any doubt, everything should be done so that an objective picture of what happened is created, so that we know what happened," Putin said at a meeting with Maksim Sokolov, his Transport Minister and the head of the Russian commission investigating the causes of the crash.
Putin did not address speculation about the cause of the disaster, and the Kremlin said separately that it would be "improper" to comment before investigators had reported.
Earlier, Smirnov said the "only possible explanation" for the crash was a "purely mechanical external impact". When asked if the plane could have been brought down by terrorists, he said that "anything was possible".
Smirnov says the plane dropped 300km/h in speed and 1.5km in altitude one minute before it crashed. "This isn't flying, it's falling. Apparently, the plane sustained damage before this [and] that became the reason for the fall," Smirnov said.
Abdel Hamid, a spokesman for Egypt's Civil Aviation Ministry, said that "external factors" could mean many things, "not only a bomb or a terrorist attack".
The potential findings of the investigation into the crash have implications for both Cairo and Moscow. A terrorist attack on tourists could prove disastrous for the Egyptian travel industry, while for Russia it could rally the public behind the air war against Islamists in Syria. A finding of mechanical or human failure, however, would raise questions about the state of Russia's aviation industry.
The Sinai affiliate of Isis (Islamic State) has claimed responsibility for bringing the plane down, but US officials dismissed the suggestion.
Meanwhile, it emerged that Metrojet owes its staff two months in unpaid wages and has suffered at least two serious accidents in the past five years. Kogalymavia, the legal entity that owns the brand name, owes its employees up to 70 million rubles ($160,000) in arrears, Alexander Snagovsky, the company's general director, said. The family of Sergei Trykhachyov, the co-pilot on Flight KGL9268, said the last monthly wage he received was for July.
In 2010, one of Kogalymavia's Tupolev planes leased to an Iranian carrier made a hard landing and broke up and caught fire, injuring 46 passengers. In 2011, three people died after one of its Tupolevs caught fire on the runway in northern Russia on New Year's Day.
St Petersburg city governor Georgy Poltavchenko yesterday said his administration would pay NZ$22,700 compensation to the families of each crash victim.
Questions over crash
On the possible use of a missile:
Aviation expert David Gleave says it is not "necessarily credible" for a group such as the Isis affiliate, which has claimed credit for downing the aircraft, to have launched a missile. "Essentially to get to that altitude, you'd need a very large missile on the ground and a fire control radar system. There are not many countries in the world that produce missiles capable of getting to that altitude and unless they have effectively stolen them in various raids ... it's not necessarily credible that they've actually got hold of those weapons. The wreckage trail does not look consistent at this stage with a normal shoot-down."
On the possibility of terrorism:
Aviation expert Michel Polacco said terrorism was the most likely cause. "A break-up of the plane mid-flight that results in the type of debris we have seen can only come from a serious blow to the plane's structure," and most likely an explosion. "It can be due to technical causes, but that is very unlikely and has rarely occured. That leads us to the terrorist line of inquiry, of a bomb that can have such effects."
On the Isis affiliate's claim of responsibility:
Zack Gold, a regional security expert, told the Guardian that if a bomb had been planted on the plane, it would suggest security systems at Sharm el-Sheikh airport had been infiltrated or compromised: "The group does not have a history of major fabrications, but at the same time it's curious that they would make this claim without providing any kind of evidence. They have military capabilities, but to carry out this kind of terrorism they would have to display organisation they haven't shown." Cornell law professor Jens David Ohlin told the Guardian: "Isis has so far focused on acquiring territory and grasping at the trappings of statehood rather than acting like a traditional terrorist organisation."
On possible damage to the fuselage:
The Kommersant cited anonymous aviation experts saying that the Airbus A321 may have been destroyed by "explosive decompression of the fuselage". A similar wreckage pattern was seen following the 1997 destruction of an Antonov An-24 near Cherkessk in the Russian North Caucasus. Experts concluded deep corrosion of the fuselage had caused the fuselage to rupture in midair. Kommersant's sources said that kind of disaster is unlikely in a properly maintained, modern aircraft. An isolated blast in the luggage compartment probably would not have been enough to destroy the aircraft, but a bomb in the pressurised passenger cabin could well have caused the shockwave that broke up the fuselage. An alternative theory is that if an engine was destroyed by malfunction, fragments could have spun off and smashed through the fuselage.
