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

Azerbaijan on Thursday observed a nationwide day of mourning for the victims of the plane crash that killed 38 people and left all 29 survivors injured as speculation mounted about a possible cause of the disaster,

The Azerbaijan Airlines Embraer 190 flight left Baku, Azerbaijan, on Christmas to Grozny, Russia. Instead, the plane crashed in Aktau, Kazakhstan.