Azerbaijan Airlines says the jet that crashed in Kazakhstan on Christmas Day experienced “physical and technical external interference,” according to an early investigation, as questions swirled about Russia’s possible involvement in the disaster.

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.