Mobile phone footage circulating online appeared to show the Azerbaijani Airlines plane making a steep descent before slamming into the ground in a fireball in western Kazakhstan.

The Embraer 190 was traveling to Grozny, Russia, but crashed near Aktau, Kazakhstan, killing 38 people onboard. Investigators are focusing on Russian air defense as the likely cause.

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.