Experts say evidence in the Azerbaijan Airlines plane crash in Kazakhstan points to a possible midair explosion, not an encounter with a flock of birds.

The Kremlin said Putin had "offered his apologies that the tragic incident had occurred in Russia's airspace."

Russian President Vladimir Putin apologised to Ilham Aliyev, the president of Azerbaijan, on Saturday for what the Kremlin said was a "tragic incident" in Russian airspace.

Russia has published a festive video of Santa Claus becoming a victim of Russian air defence against the backdrop of the tragic crash of an Azerbaijan Airlines passenger plane in Grozny, with growing evidence pointing to Russian air defence as the cause.

Kazakhstan, Azerbaijan and Russia all opened investigations into the cause of the crash of Azerbaijan Airlines Flight 8243.

Russia's aviation watchdog said the captain of the plane had been offered other airports at which to land, but had chosen Kazakhstan's Aktau.

The White House said Friday there were "early indications" that Russian air defenses downed an Azerbaijan Airlines flight in Kazakhstan.

Several airlines have announced the suspension of flights to Russian cities, after an Azerbaijan Airlines plane with 67 people on board crashed.

El Al, the national airline of Israel, has temporarily suspended flights to Moscow following the crash of the Azerbaijan Airlines Embraer ERJ 190, which resulted in the deaths of 38 people. Israeli state media identifies “developments in Russia’s airspace” as the reason for the suspension.

Putin did admit that Russian air defences were at work when the passenger plane tried to land in Grozny before crashing, and the Kremlin said Putin apologised to Azerbaijani leader Ilham Aliyev over the "tragic incident" in a phone call, but did not say Russian air defence shot the plane.

Russian President Vladimir Putin has apologized to his Azerbaijani counterpart for what he called a "tragic incident" following the crash of an Azerbaijani airliner in Kazakhstan that killed 38 people.