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.

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,

The U.S. Department of State has a Level 2 advisory for Azerbaijan, recommending that travelers exercise "increased caution."