An investigation into the deadly crash of an Azerbaijan Airlines flight in Kazakhstan earlier this week came after the passenger plane experienced “physical and technical external interference,” the carrier said on Friday.

The plane, which crashed in Kazakhstan this week, went down “due to external physical and technical interference,” according to the investigation’s preliminary findings.

The cause of the crash of Azerbaijan Airlines flight J2-8243 near the city of Aktau, Kazakhstan, is still unknown. The Kremlin has so far been tight-lipped, prompting questions over its messaging.