International investigators on Sunday began probing why a Russian airliner carrying 224 people crashed in Egypt’s Sinai Peninsula, killing everyone on board, as rescue workers widened their search for missing victims.

The plane broke apart “in the air”, a senior official with Russia’s Interstate Aviation Committee said on Sunday.

“The disintegration happened in the air and the fragments are strewn over a large area,” committee chief Viktor Sorochenko was quoted as saying by RIA-Novosti news agency in Cairo, where he is part of an international panel of experts from Russia, Egypt, France and Ireland.

Air France and Lufthansa said on Saturday they will stop flying over the Sinai peninsula. However, other airlines, including British Airlines, have said that they will continue to fly over Sinai.

Egypt’s President Abdel Fattah al-Sissi urged people to await the outcome of the investigation to determine the cause of the crash, after the ISIS jihadist group claimed it brought down the A321.

“In such cases, leave it to specialists to determine the cause of the plane crash because it is a subject of an extensive and complicated technical study,” state news agency MENA quoted Mr Sisi as telling a gathering of Army officers.

At the crash scene in the centre of North Sinai, in the Wadi al-Zolomat area, numerous blackened parts of the plane were scattered, with the smell of burnt metal lingering in the air, an AFP correspondent reported.

A few metres further lay a tiny red jacket, probably of a child, underlining the horror of Saturday’s tragedy that killed 17 children including a 10-month-old girl.

An Army officer involved in search efforts said rescue crews had recovered 163 bodies so far, including that of a girl found eight kilometres from the main wreckage.

Russian transport authorities ordered the Kogalymavia airline, whose jet crashed, to check all its Airbus 321 planes as part of an urgent safety review.

Flags were flying at half mast in Russia on Sunday and entertainment television programmes were cancelled as part of a national day of mourning for the victims, most of them Russians, aged from 10 months to 77 years.

Cairo and Moscow have downplayed the claim from the ISIS branch in Egypt that it brought down the aircraft.