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.

A French aviation expert said that the crash in Aktau on Christmas Day was “reminiscent” of the Malaysian Airlines flight which was downed by a Buk surface-to-air missile by Russia-backed rebels over eastern Ukraine a decade ago, killing all 298 people on board.

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.