The Russian airline whose jet crashed in Egypt killing everyone on board says the crash could not have been caused by a technical fault or a mistake by the pilot or the crew.
Kogalymavia Deputy Director Aleksandr Smirnov said on November 2 that the crash could only have been the result of some other "technical or physical action" that caused it to break up in midair.
The Airbus A321-200 came down over the Sinai Peninsula on October 31 after taking off from the resort of Sharm el-Sheikh en route to St. Petersburg.
All 224 people on board, most of them Russians, were killed in the deadliest air disaster in Russian and Soviet aviation history.
Describing the crash as an "enormous tragedy," President Vladimir Putin called on investigators to build an "objective picture" of what happened.
Russian transport authorities earlier said the airliner "broke up in midair," adding that it is too early to say what caused the jet to crash.
Viktor Sorochenko, head of Russia's Interstate Aviation Committee, said on November 1 that "the plane broke up in midair and its fragments are scattered over a large area of about 20 square kilometers."
All 217 passengers -- including at least 24 children -- and seven crewmembers were killed when the plane crashed in a desolate area between the Sinai Peninsula's northern coastal city of Arish and the town of Hasna.
Almost all the victims were Russians, many returning to St. Petersburg and nearby towns after a vacation in the popular Red Sea resort.
A Russian Emergency Situations Ministry plane carrying 144 bodies of crash victims arrived in St. Petersburg early on November 2. The remains were taken by motorcade to a local crematorium for identification. More remains are to be brought back later in the day.
A local affiliate of the Islamic State (IS) militant group on October 31 claimed it had downed the plane, but it did not say how. Russian and Egyptian officials have said there is no evidence the Airbus A321 was shot down or blown up.
Several international airlines have suspended flights over the Sinai Peninsula as a precaution while the investigation is being conducted.
Russian Transport Minister Maksim Sokolov and Emergency Situations Minister Vladimir Puchkov inspected the crash site after arriving in Egypt, along with the head of the Russian civil aviation agency, Aleksandr Neradko.
A day after stunned relatives struggled with grief and loss at Pulkovo Airport in St. Petersburg, Russia held an official day of mourning on November 1, as decreed by President Vladimir Putin. Flags flew at half-staff and television stations canceled entertainment programs.
Russians brought flowers and stuffed toys to the airport in a show of solidarity and sadness over the lost lives. Yelena Vikhareva, 48, had no relatives on the plane but went with her son to lay flowers, saying "pain is piercing her heart."
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State television showed heartrending pictures taken by vacationers killed in the crash -- a little girl photographed before boarding the flight, a 22-year-old woman's seaside bathing-suit shot on her first trip to Egypt.
Special prayer services were held and Patriarch Kirill, the head of the Russian Orthodox Church, said the tragedy touched all Russians.
A crisis center worked through the night in St. Petersburg, providing counseling and other assistance to families of people believed to be on board the plane. Officials were interviewing relatives and taking DNA samples to assist with the identification of the bodies.
State-run Russian news agency RIA Novosti said it was the deadliest disaster in the history of Soviet and Russian aviation, surpassing a 1985 crash in Uzbekistan that left 200 people dead.
Interfax news agency reported that Russia's transport safety watchdog, Rostransnadzor, ordered Kogalymavia -- which operates under the name Metrojet -- to ground its Airbus A321s for the time being, but RIA quoted an official at the airline as saying it had not received such an order.
Egyptian officials said both "black box" flight-data recorders have been recovered and sent for expert examination. It remained unclear why Flight 9268 crashed in calm weather.
The IS affiliate, Wilayat Sinai, made its claim of responsibility for the crash via social media, including Twitter and Telegram. "The fighters of the Islamic State were able to down a Russian plane over Sinai province that was carrying over 220 Russian crusaders," its statement read.
The disaster came just over one month after Russia launched a campaign of air strikes in Syria that among other groups have targeted IS, one of the foes of President Bashar al-Assad in the country's more than four-year civil war.
Sokolov said on October 31 that the militants' claim "can't be considered accurate," adding that authorities in Egypt "have no such information that would confirm such insinuations."
Egyptian Prime Minister Sherif Ismail said on October 31 that there did not appear to be any unusual activity behind the crash but that the facts would not be clear until further investigations had been carried out.
Western news agencies quoted experts as saying militants in the area were not believed to have missiles capable of hitting a plane as high as the Russian jet, which Egypt's Civil Aviation Ministry said was at an altitude of 9,400 meters when it vanished from radar screens 23 minutes after takeoff.
According to FlightRadar24, a Sweden-based flight-tracking service, the aircraft was descending rapidly at about 1,800 meters per minute when the signal was lost.
Russian aviation regulator Rosaviatsia said on October 31 that without evidence, there were no grounds to blame the crash on a technical failure, an error by the crew, or "external" actions -- meaning a bombing or other deliberate attack.
"Until there is reliable evidence about the circumstances of what happened, there is no sense in putting forward and discussing any versions," Rosaviatsia said in a statement.
Russian network NTV broadcast an interview with the former wife of co-pilot Sergei Trukachev in which she said that he had complained about the technical condition of the aircraft in a telephone conversation shortly before the plane took off.
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A senior Russian aviation official said on November 1 that the Airbus had been certified to fly, and an Egyptian official who inspected the plane said it was in good technical condition before takeoff.
France's BEA accident investigation agency said a team including two BEA investigators and six technical advisers from Airbus, was arriving on November 1 and would be joined by two investigators from its German counterpart BFU, as well as four from the Russian aviation agency.
The Airbus A321-200 jet was designed in France and built in Germany in 1997, and had flown 56,000 hours in nearly 21,000 flights. Airbus said it had been operated by Metrojet since 2012.
Russia's federal Investigative Committee launched a criminal investigation and searched the offices of Kogalymavia in Moscow on October 31, seizing documents.
RIA Novosti reported that the case had been brought under an article regulating "violation of rules of flights and preparations for them." But such cases are common after air crashes and do not necessarily imply suspicion of guilt.
Kogalymavia has been operating since 1993 and is based in the city of Kogalym, in Russia's Tyumen region.
The RIA and Interfax news agencies quoted a spokeswoman for Kogalymavia as saying that there were no grounds to blame human error for the crash as the pilot had 12,000 hours of flying experience. She added that the plane had been fully serviced.
Roughly 3 million Russian tourists travel to Egypt every year, mostly to the Red Sea resorts in the Sinai or on the mainland.
With reporting by RFE/RL's Russian Service, Reuters, AFP, dpa, RIA Novosti, TASS, and Rossia-24