Russian President Vladimir Putin has apologized to Azerbaijani President Ilham Aliyev following the crash of an Azerbaijan Airlines plane in Kazakhstan that resulted in 38 fatalities, according to the Kremlin.

Four sources with knowledge of the preliminary findings of Azerbaijan's investigation told Reuters that Russian air defences mistakenly shot it down.

Two U.S. military officials told NBC News that they had intelligence indicating that Russians may have misidentified the plane and shot it down.

Russian President Vladimir Putin apologized for the deadly Azerbaijan Airlines Flight 8243 crash on Christmas but did not take responsibility for causing it as an investigation continues into the matter.

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.

Azerbaijan’s President Ilham Aliyev has accused Russia of accidentally shooting down an airliner on Christmas Day in a disaster that killed 38 people, and covering up the cause.

Azerbaijan's president has accused Russia of shooting down a plane that recently crashed under controversial circumstances. The allegation comes amid heightened tensions in the region, with both countries exchanging accusations over security and sovereignty issues.