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.

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, with some experts saying that the airliner was damaged by Russian air defense fire.

We will never forget the beloved people we lost in the crash of the Embraer 190 aircraft,” said Azerbaijan Airlines in a statement posted online on Boxing Day. The pro-government AnewZ news station cited Azerbaijan officials as saying shrapnel from a Russian missile was responsible.