T hursday 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. Video posted by CNN shows the plane crash-landing, exploding into a fireball and plumes of black smoke.

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.

Russian air defenses, rather than a bird strike, likely caused the downing of an Azerbaijan Airlines flight, killing 38 people.

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.

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