Azerbaijan President Ilham Aliyev said Russia is behind the Christmas Day crash of an Azerbaijan Airlines plane in Kazakhstan, which killed 38 of the 67 people aboard. The motives of the incident remain unclear.

Azerbaijan’s President Ilham Aliyev said Sunday that the Azerbaijani airliner that crashed last week was shot down by Russia, albeit unintentionally, and criticized Moscow for trying to “hush up” the issue for days.

Early indications suggest a Russian anti-aircraft system may have downed the passenger jet that crashed in Kazakhstan, a US official told CNN, as authorities recovered a second black box that they hope will shed light on the cause of the disaster that killed dozens of people.

The probe into the Azerbaijan Airlines crash in Kazakhstan is examining the conduct of air traffic controllers after the aircraft encountered difficulty, a source said.