Azerbaijan Airlines plane crash, likely caused by Russian air defense, shines light on a glaring issue the Kremlin has long swept under the rug.

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 extremely rare publicised apology from Putin was the closest Moscow had come to accepting some blame for Wednesday's disaster, although the Kremlin statement did not say Russia had shot down the plane.