The Kremlin on Thursday warned against speculating what may have caused an Azerbaijan Airlines flight to crash, killing 38 of the 67 on board, after an aviation expert said evidence indicated that a Russian anti-missile battery may have brought down the passenger plane.

"No one claims that it was done on purpose," an Azerbaijan official told Reuters. They added their government "expects the Russian side to confess."

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.