The White House indicated early evidence points to the crash, which killed 38, being caused by a Russian weapon.

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.

Vladimir Putin admitted Saturday Russian air defence was working when an Azerbaijani Airlines plane tried to land in Grozny before crashing, breaking the Kremlin's silence as speculation mounted Russia may have accidentally shot the plane.