The Azerbaijan Airlines plane flew hundreds of miles off its scheduled route from Baku to Grozny, and crashed on the eastern shore of the Caspian Sea. Russia's aviation watchdog said a bird strike might have been the cause.

The flight was en route from the Azerbaijani capital of Baku to Grozny, in Russia’s south, when it diverted and attempted an emergency landing in Kazakhstan.

Thursday is an official day of mourning in Azerbaijan as an investigation is underway to determine what caused an airplane carrying 67 passengers to crash on Christmas Day in Kazakhstan, killing 38 and leaving at least 29 survivors.

By Nailia Bagirova and Gleb Stolyarov BAKU (Reuters) -Russian air defences downed an Azerbaijan Airlines plane that crashed in Kazakhstan, killing 38 people, four sources with knowledge of the preliminary findings of Azerbaijan's investigation into the disaster told Reuters on Thursday.

A U.S. official tells NBC News there are early indications that the passenger plane that crashed in Kazakhstan may have been hit by a Russian anti-aircraft system. The official said if it turns out to be the case,

There are early indications that a Russian anti-aircraft system may have struck the Azerbaijan Airlines plane that crashed in Kazakhstan, a U.S. official told ABC News.