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Relatives of victims of Metrojet's Airbus A-321 plane with registration number EI-ETJ that crashed in Egypt, mourn at Crowne Plaza hotel near Pulkovo airport in St. Petersburg, Russia, Oct. 31, 2015. Peter Kovalev/Reuters

UPDATE 8:45 p.m. EDT: Russian officials scheduled several days of mourning for the victims of the crash of a Russian Airbus A321 en route from Sharm el-Sheikh to St. Petersburg, Tass reported early Sunday. Russian officials said the bodies of 150 of the 224 victims of the crash have been recovered, and Egyptian officials said they are ready to begin transporting the dead back to Russia.

UPDATE 6 p.m. EDT: The co-pilot of the Russian passenger plane that crashed in the Sinai Saturday complained about the Airbus A321's condition before takeoff, reported. Natalia Trukhacheva said her ex-husband was an experienced pilot and told his eldest daughter the aircraft "left much to be desired."

UPDATE 5:45 p.m. EDT: Air France-KLM and Lufthansa Saturday decided against flying over the Sinai Peninsula until it can be determined whether terrorism was involved, Reuters reported. "We took the decision to avoid the area because the situation and the reasons for the crash were not clear," a Lufthansa spokeswoman said. "We will continue to avoid the area until it is clear what caused the crash."

An Air France spokeswoman confirmed the carrier "has set up, as a precaution, measures to avoid flights over the zone of Sinai," the spokeswoman for the carrier said.

Original post:

A Russian airliner crashed in the Egyptian Sinai Saturday, killing all 224 on board, the Guardian reported. An Egyptian branch of the Islamic State terror group, aka ISIS, claimed responsibility shortly afterward, but officials from Russia and Egypt rejected the idea and said the event was likely caused by a mechanical failure in the plane, which was bound for St. Petersburg from the Red Sea resort of Sharm el-Sheikh.

"We are in close touch with our colleagues from Egypt and their air traffic authorities, and they have nothing at the moment which could confirm such fabrications," Russian Transport Minister Maxim Sokolov told the BBC. Russia has dispatched several planes to the central Sinai to assist Egypt with recovery and possible rescue efforts.

Officials have recovered the airliner's black box, which the BBC reported will illuminate the cause of the crash.

The chairman of Egypt's state airport company said the plane had gone through technical checks at Sharm el-Sheikh's airport prior to the flight, CNN reported. The only previous incident involving the plane happened in 2001, when the Airbus A321's tail sustained damage upon hitting the runway, and required repair.

Russian media outlets such as Russia 24 reported that the pilot of the downed airplane had reported technical problems and requested a landing at the nearest airport before it went missing. Some experts have speculated that if the plane were downed by an attack rather than a malfunction, it would have been while it was landing.

Russian President Vladimir Putin demanded an investigation into the circumstances of the crash and set an official day of mourning Sunday for those who died.

A statement reportedly from the militants claiming responsibility circulated on Twitter Saturday morning: "Soldiers of the caliphate were able to bring down a Russian plane above Sinai Province with at least 220 Russian crusaders aboard," it said in a translation by the Guardian. "They were all killed, praise be to God. O, Russians, you and your allies take note that you are not safe in Muslims' lands or their skies.

"The killing of dozens daily in Syria with bombs from your planes will bring woe to you," the statement added. "Just as you are killing others, you too will be killed, God willing."

Several experts joined officials in speculating that the Egyptian members of ISIS in the Sinai lack the weaponry necessary to down an Airbus traveling at over 30,000 feet.