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.

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.

After an Azerbaijan Airlines jet crashed in Kazakhstan, speculation mounted about why the plane went down and whether possible Russian air defense action may have played a role.

The Azerbaijan Airlines flight from Baku to Grozny in Russia was carrying 67 people when it crashed near Aktau early Wednesday. Kazakh officials said 29 people survived.

There are dozens of survivors and many feared dead after an Azerbaijan Airlines flight crashed down in Kazakhstan.

The crash of an Azerbaijani airliner in Kazakhstan has killed 38 of 67 people on board. Azerbaijan Airlines’ Embraer 190 was en route from Azerbaijani capital Baku to the Russian city of Grozny in the North Caucasus on Wednesday when it was diverted for reasons that aren’t fully clear yet.

A passenger plane flying from Azerbaijan to Russia with 67 people on board crashed in Kazakhstan Wednesday, authorities said.