Azerbaijan held a day of mourning on Thursday for the dozens of victims of an airliner crash in Kazakhstan, as questions were being asked over the cause of the disaster.

The flight was en route from the Azerbaijani capital of Baku to Grozny, in Russia’s south, when it diverted and attempted an emergency landing in Kazakhstan.

Azerbaijan on Thursday observed a nationwide day of mourning for the victims of the plane crash that killed 38 people and left all 29 survivors injured as speculation mounted about a possible cause of the disaster,