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,

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.

Russia and Kazakhstan have tried to calm speculation about the cause of the Azerbaijan Airlines plane crash, following claims that it was shot down by Russian air defence systems.On Thursday, Moscow urged calm as its foreign minister said it would be wrong to draw conclusions before an investigation into the crash was complete.