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.

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.

Dozens of people were killed on Wednesday after an Azerbaijan Airlines flight crashed near the Kazakhstani city of Aktau, according to officials.