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.

The flight was heading from Azerbaijani capital Baku to the Russian city of Grozny when the crash occurred. The plane crashed while trying to make an emergency landing at the Aktau airport in Kazakhstan. Among the 29 survivors were two children.