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

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.

The Kremlin has said that the Russian president "apologized for the tragic incident" and expressed his "deep and sincere condolences" to the victims' families.