An Azerbaijani airliner has crashed in Kazakhstan after being diverted, killing 38 of 67 people on board. Some experts alleged that the plane went down after being hit by Russian air defense systems. Some things to know about the crash and the speculation about a possible cause:

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.

Aviation experts say that Russian air defense fire was likely responsible for the Azerbaijani plane crash the day before that killed 38 people and left all 29 survivors injured.

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.

Thirty eight people were killed and dozens survived a plane crash in Kazakhstan while traveling to southern Russia, according to local officials, as speculation swirls online that Russia could somehow have been responsible for the crash.