Technical faults were not to blame for the Russian plane crash on Saturday, officials have said, adding to speculation that the aircraft may have been brought down by militants.
A spokeswoman for Kogalymavia, which operated the Metrojet flight, said on Monday that it is "impossible" that a technical fault caused its jet to break up, killing 224 people.
An airline executive said that the only reasonable explanation for the crash in Egypt was "an external influence." Pilot error was also ruled out as a cause.
Yet a source in the Egyptian investigation committee said that the plane was not struck from the outside, Reuters reports.
During a press conference on Monday, the cause of the crash was attributed to "some kind of impact", causing the plane to start falling apart in mid-air as it flew over Egypt.
They added: "This plane was in excellent technical condition."
The conference was held as the bodies of those who died in the crash began arriving in St Petersburg today.
On Sunday, terrorist group, IS, released footage online purporting to be "proof" that they were responsible for the disaster.
At the press conference on Monday, officials refused to say whether the plane was the target of a terrorist attack, adding: "It could be anything so let's just wait for the official results."
Responding to "footage" released by IS, an airline spokesman said: "You can't rule out anything, but the video that you can see on the internet clearly indicates that it's a fake."
Contradictory reports are circulating from Russian and Egyptian authorities.
While Egyptian officials say that the pilot reported a technical problem and wanted to make an emergency landing at the nearest airport, a Metrojet official says that its crew did not send a distress call or contact Egyptian traffic controllers before the plane crashed.
Two black boxes have been recovered from the crash scene, but investigators have yet to determine the cause of the disaster.
On Sunday, IS released a statement that said: "Soldiers of the Caliphate were able to bring down a Russian plane above Sinai Province with at least 220 Russian crusaders aboard.
"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. Just as you are killing others, you too will be killed, God willing."
Story continues after slideshow...
The Airbus A-321 was bound for St Petersburg crashed shortly after taking off from the resort of Sharm el-Sheikh.
It was carrying 221 Russians and three Ukrainians, mainly tourists returning from their holidays.
There were 17 children on board.
Flight 7K9268 vanished from radars just 23 minutes after take-off.
Although the so-called Islamic State terror group tried to claim responsibility for the crash, many were sceptical, with one expert calling it "almost certainly nonsense".
The aircraft belonged to Russian airline Kogalymavia, also known as Metrojet, and was carrying mainly Russian tourists at the time.