After an Azerbaijan Airlines jet crashed in Kazakhstan, speculation mounted about why the plane went down and whether possible Russian air defense action may have played a role.

Russian aviation authorities said the Azerbaijan Airlines plane had hit a flock of birds. But some experts cast doubt on that account, pointing to footage showing apparent holes in the fuselage.

U.S. officials say Russia could be behind a passenger plane crash in Kazakhstan that left dozens dead on Christmas Day. U.S. officials say it looks like the plane was hit by a Russian air defense system,