A Russian passenger airliner carrying 224 passengers and crew from the Egyptian Red Sea resort of Sharm el-Sheikh to St Petersburg in Russia crashed soon after taking off early Saturday, killing everyone onboard, officials said. The plane crashed in a mountainous region in Egypt’s Sinai peninsula.

On Sunday, Russia's transport minister and a team of investigators arrived in Cairo to help Egyptian authorities determine the cause of the crash, reported Reuters.

Here's what we know so far:

· Flight KGL9268, an 18-year-old Airbus A321-23, belonged to the private Kogalymavia airline based in west Siberia. Everyone on board was Russian, except for three people from Ukraine and one Belarusian. Most of the 100-plus bodies recovered so far were severely burnt.

· The plane lost contact with Egyptian air traffic control 23 minutes after it taking off. It was flying at 31,000 feet when it suddenly began to descend. Flightradar24, which tracks air traffic, said the plane had been descending at a rate of 6,000 feet per minute just before it disappeared from radar.

· Egyptian authorities have recovered the plane's two black boxes, which have been sent for analysis. The authorities have also denied any abnormal signs before the plane disappeared, like a request for a change of route. Kogalymavia has also insisted there were no grounds to blame it on human error, and that the plane was in good working order with experienced pilots.

· The crash site is in the Hasana area in Egypt’s Sinai peninsula, which is mostly a closed military zone, following a long-running insurgency by militants close to Islamic State against Egyptian President Abdel Fattah-el-Sisi’s government.

· Hours after the crash, a militant group affiliated to the Islamic State in Egypt has claimed responsibility for bringing the plane down. Egyptian and Russian officials have refuted these claims, saying experts confirmed that militants could not down a plane at 30,000 feet.

· Three airlines – Emirates, Air France and Lufthansa – have decided not to fly over the Sinai Peninsula until more information is available.

Here's what we don't know yet:

· Investigators are still working to establish the cause of the crash. They were checking fuel samples from the plane’s last refuelling stop in the Russian city of Samara. In 2011, a Kogalymavia plane’s fuel tank exploded before departure, killing three people.

· The possibility of a bomb having been planted on the plane has not been ruled out, reported the New York Times.