An Azerbaijan Airlines flight that crashed in Kazakhstan on Wednesday was downed by a Russian air defence system, four sources in Azerbaijan with knowledge of the investigation told Reuters.

An Embraer passenger jet crashed near the city of Aktau in Kazakhstan on Wednesday, killing 38 people, after diverting from an area of Russia in which Moscow has used air defence systems against Ukrainian drone strikes in recent months.

Azerbaijan Airlines flight J2-8243 had flown hundreds of miles off its scheduled route from Azerbaijan's Baku to Grozny, in Russia's Chechnya, to crash on the opposite shore of the Caspian Sea, after what Russia's aviation watchdog said was an emergency that may have been caused by a bird strike.

Officials did not immediately explain why it had crossed the sea, but the crash came after Ukrainian drone strikes this month hit the Chechnya region of southern Russia. The nearest Russian airport on the plane's flight path was closed on Wednesday morning.

Russian, Azerbaijani and Kazakhstani officials have all called for investigations into the crash.