It comes as the head of Russia's civil aviation agency says the situation in Grozny, the plane's destination, was "very complicated" at the time.

Experts say evidence in the Azerbaijan Airlines plane crash in Kazakhstan points to a possible midair explosion, not an encounter with a flock of birds.

The national airlines of Azerbaijan and Kazakhstan have suspended some flights to Russia after evidence suggested an Azerbaijani plane had been downed by Russian air defence systems. The Kazakh airline,