A Russian passenger plane - Airbus A321 - crashed in Egypt's Sinai on Saturday, killing all 224 people on board. The plane was travelling from Sharm El-Sheikh to St Petersburg in Russia.
Since the crash, both Russian and Egyptian officials have released a number of statements on the probable cause of the crash.
The statements, at times conflicting, are mainly speculative, since the black boxes have yet to be decoded.
The following points are taken from official statements so far:
1) The plane broke apart in midair
Russia's Interstate Aviation Committee Chief Viktor Sorochenko said on Sunday that "the disintegration [of the plane] happened in the air and the fragments are strewn over a large area.”
Sorochenko was quoted by RIA-Novosti news agency while in Cairo, where he is part of an international panel of experts from Russia, Egypt, France and Ireland who are looking into the accident.
2) The pilot did not make contact with the air traffic control
Pilot Ayman El-Mokadem, who heads a separate Egyptian committee to determine the cause of the crash, made initial statements on Saturday to the effect that the pilot sensed technical failure and reported it to the air traffic controllers.
However, since then both Egypt's civil aviation minister and Russian officials have denied that the pilot made any emergency calls.
3) The plane was in "excellent" condition
Alexander Smirnov, deputy general director of the airline, Kogalymavia, to which the jet belonged, said at a Monday press conference in Moscow that: "the plane was in excellent condition."
The Irish Aviation Authority also said on Monday the plane was registered in Ireland, and regulators there found its safety documentation in order earlier this year, AP reported.
The Airbus A321 was owned by Irish firm Willmington Trust SP Services (Dublin) Ltd and leased to Russian airline Metrojet.
The aviation authority said that because the plane was Irish-registered, "in April/May 2015, the Irish Aviation Authority conducted an annual review of the aircraft certifications in support of its annual Certificate of Airworthiness renewal process and all certifications were satisfactory at that point in time."
4) The plane was previously damaged
Kogalymavia's deputy general director for engineering, Andrei Averyanov, said on Monday that in 2001 the plane's tail section had struck the tarmac on landing but was later fully repaired.
Ayeryanov said that the 2001 incident could not have been a factor in the crash.
However, previous damage to a plane, even if repaired, could in rare circumstances cause a plane to crash, even decades later.
5) The only possible explanation is an external impact
"We rule out a technical fault of the plane or a pilot error," said Smirnov on Monday. "The only possible explanation could be an external impact on the airplane," he added.
But when pressed for more details about the type of impact and what could have caused it, Smirnov insisted that he was not at liberty to discuss details because the investigation was ongoing, AP reported.
He also did not explain whether he meant something had hit the plane or that some external factor caused the crash.
6) Flight recorders show the jet was not struck from outside
The Russian plane was not struck from the outside, a source in the committee analysing the flight recorders told Reuters on Monday, basing his comments on the preliminary examination of the black boxes recovered from the Airbus A321.
7) There is no direct evidence of terrorism yet
US Director of National Intelligence James Clapper said Monday he knew of no "direct evidence" that terrorism was to blame for the weekend plane crash of a Russian passenger plane in Egypt, AFP reported.
Speaking at a Washington defence summit, Clapper said it was "unlikely" that the Islamic State group had the capacity to carry out such an attack, but added "I wouldn't rule it out."
"We don't have any direct evidence of a terrorist element yet," he said.
8) No cause should be ruled out
There are not yet any grounds to rule out any single theory, the Kremlin's spokesman Dmitry Peskov said on Monday, replying to a question about whether a terrorist attack could be to blame, Reuters reported.