American satellites detected heat around the Russian Airbus A321 before it crashed in Egypt on Saturday, suggesting an explosion might have caused the tragedy.
As a missile strike has been ruled out as neither a launch nor an engine burn have been detected by the satellites, the infrared activity might have been caused by an engine explosion or a bomb, experts suggested, adding that it was too early for conclusions.
"It doesn't tell us if it was a bomb... or if somebody had a fight in the airplane with a gun. There is a whole raft of things that could happen in this regard," said aviation analyst Paul Beaver.
Although Beaver suggest a fuel tank or engine explosion could have been the cause, he says that engines are designed to contain any malfunctions within themselves.
Egyptian investigators in cooperation with Russian experts will analyse the contents of the two flight data recorders found at the crash site on the Sinai Peninsula.
Egyptian civil aviation minister Hossam Kamal said it "will take some time" to produce the final report and that the committee "has all the tools and experts to deal with the investigation".
The 18-year old aircraft operated by Russian airline Metrojet crashed 23 minutes after take-off from the Egyptian holiday resort Sharm el-Sheikh. It carried 224 people, mostly holidaymakers returning to St Petersburg.
The jet received its airworthiness certificate in Ireland, where it was registered, earlier this year and its engines undergone inspection only a week before the disaster.
In 2001, the jet’s tail was damaged during landing, but the airline said it has since been completely fixed. Faulty tail-strike repairs have caused at least two catastrophic crashes in the past.
Egypt's civil aviation ministry said on Tuesday there were no facts to substantiate assertions by Russian officials that the airliner broke up in mid-air.
Spokesman Mohamed Rahmi confirmed that no distress call had been received before the crash, which left pieces of wreckage scattered over more than three kilometres of desert.
"No communication from the pilot was recorded at the navigation centres requesting anything," he told Reuters.