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.

Russian aviation authorities said the Azerbaijan Airlines plane had hit a flock of birds. But some experts cast doubt on that account, pointing to footage showing apparent holes in the fuselage.

Even as a probe was starting of the crash of an Azerbaijan Airlines airliner in Kazakhstan, speculation was mounting about why the plane went down.

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.

National flags were lowered across Azerbaijan, traffic across the country stopped at noon, and signals were sounded from ships and trains as the country observed a nationwide moment of silence.

Thursday is an official day of mourning in Azerbaijan as an investigation is underway to determine what caused an airplane carrying 67 passengers to crash on Christmas Day in Kazakhstan, killing 38 and leaving at least 29 survivors.

Azerbaijan is observing a nationwide day of mourning for the victims of the air crash that killed 38 people and left all 29 survivors injured as speculation mounted about a possible cause of the crash

Officials in Russia and Kazakhstan are urging people to wait for an investigation into the deadly Azerbaijan Airlines plane crash before assigning blame.

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.