Speculation over the cause of Russia's worst civilian aviation tragedy is snowballing after evidence emerged that the Airbus A-321 carrying holidaymakers broke up in mid-air, possibly after an explosion, and the Islamic State (IS) terrorist organisation claimed that it downed the aircraft.

All 224 passengers and crew aboad died when the Kogalymavia flight went down in Egypt's Sinai Desert on October 31 while flying mainly Russian holidaymakers home to St Petersburg from the resort of Sharm el-Sheikh. This was Russia's worst ever civil aviation disaster.

The bodies of 144 crash victims were flown back to the northern Russian city on the morning of November 2 as an investigation into the cause continues. Vehicles were transporting the bodies to a local crematorium for identification by relatives. A second flight with more bodies was due to arrive later in the day.

The aircraft was carrying 217 passengers, including at least 17 children, Russian transport officials said. There were seven crew members on board.

A group claiming to speak for the Islamic State terrorist group later posted an online statement saying that "Soldiers of the caliphate were able to bring down a Russian plane above Sinai province".

Russian Transport Minister Maksim Sokolov said the claim "cannot be considered accurate". Egyptian army spokesman Mohamed Samir also disputed the claim.

"They can put out whatever statements they want but there is no proof at this point that terrorists were responsible for this plane crash," Samir said. "We will know the true reasons when the Civil Aviation Authority in coordination with Russian authorities completes its investigation. But the army sees no authenticity to the claims."

Air France, Lufthansa, KLM and Emirates airlines said they will avoid the Sinai route as a precaution until the cause of the crash has been established.

The plane's black box has already been recovered but no official cause has been identified. However, according to early reports, the aircraft's crew was complaining about engine trouble a week earlier. Given the distribution of the wreckage, the plane appears to have broken up in mid-air, prompting additional speculation about a possible terrorist attack.

"So the fact that there was a catastrophic failure at 31,000 feet, with the aircraft falling in two pieces, suggests to me an explosion on board. So was this caused by some form of terrible accident, which is unlikely, or a bomb, which is much more likely my mind is moving in that direction rather than anything that happened on the ground," an aviation expert told the Daily Mail.

The IS claimed to have shot down the plane, but video footage purportedly released by the organisation appears to show an explosion in the rear of the plane in mid air.

Experts stress that as the plane was flying at almost 10,000 metres at the time it could not have been hit by a man-portable missile. Downing the plane would require a far more sophisticated missile system than the IS and other militant groups active in the region are known to have at their disposal.

The crew also did not send a distress signal before the plane disappeared from air traffic controllers screens, also suggesting the cause of the crash was sudden. Both Cairo and Moscow have denied there was any terrorist link to the crash.

According to sources of Russia's Kommersant newspaper, the crash could have occurred  due to explosive decompression of the cabin: the plane exploded from a sharp pressure drop at high altitude, which the cource said could have been caused by a small bomb hidden in luggage space.

Another reason for the crash could be a fatigue crack in fuselage, the source said. It was found out that in 2001, the crashed Airbus had hit the runway during the landing in Cairo airport. This incident could lead to a violation of the plane’s geometry and flight characteristics, the source said.

The plane was reported missing 23 minutes after leaving the Red Sea resort of Sharm el-Sheikh. It then plunged about 3,000m to the desert floor after flight information showed that it suffered a dramatic loss in speed. Experts put the time of the crash at 4:13am on Saturday.

If the Airbus A321 plane were suffering from double engine failure then it would have been able to glide down over some 20mins, but its fall was more rapid than that, consistent with massive mechanical failure or a mid-air break-up.

The wreckage on the ground was also spread over a wide area, which is  also consistent with a mid-air break-up.

The plane was an Airbus A321, the workhorse of the mid-haul Russian tourist industry. The aircraft was built in 1997, well within the useful life of aircraft in service in Russian air fleets. The pilot was Valery Nemov, who was described as very experienced with over 12,000 hours of flight time.

Rapid response

The Russian authorities were very fast to respond to the tragedy. Russian Prime Minister Dmitry Medvedev immediately ordered the Russia transport minister to Egypt to coordinate with the Egyptian authorities, and several Russian search and rescue teams from the Ministry of Emergency Situations (MChS) were also dispatched.

 

Medvedev tweeted in English and Russian to express his condolences to the victims families and promised them a full investigation would be carried out.

From the international leaders, French Prime Minister Francois Hollande was the first to respond, also expressing his condolences.

 

At street level, the outpouring of grief and sympathy was universal and sincere. President Vladimir Putin declared several days of mourning and flowers and toys quickly piled up on the steps of Pulkovo, St Petersburg's airport where the doomed flight was due to return.

In In Kyiv too, Ukrainians piled up flowers and lit candles for the dead together with a sign that said that the difference between Russia and Ukraine was that even as enemies the Ukrainians mourned the death of the victims of the tragedy.

Finally, Google tributes summing up the international shock and sympathy after the crash  included a black ribbon on their home page in a mark of respect for the dead.