Azerbaijan’s leader on Monday accused Moscow of carrying out a “cover up” over a passenger jet crash last month that claimed 38 lives, as relations sour between the two neighbors.

Azerbaijan’s President Ilham Aliyev says the Azerbaijani airliner that crashed last week was shot down by Russia, albeit unintentionally.

Four sources with knowledge of the preliminary findings of Azerbaijan's investigation told Reuters that Russian air defences mistakenly shot it down.

Two U.S. military officials told NBC News that they had intelligence indicating that Russians may have misidentified the plane and shot it down.

In the crash’s aftermath, Azerbaijan has unleashed rare and stinging criticism of Russia, with the country’s president saying Moscow’s response has caused “surprise, regret and rightful indignation.”

"The blame for this disaster lies with representatives of the Russian Federation," Ilham Aliyev said on Jan. 6.

Azerbaijan's president has confronted Putin over the devastating plane crash that killed 38 people on Christmas Day.

We demand justice, we demand punishment for those responsible, and we demand full transparency, — said the President of Azerbaijan, Ilham Aliyev, regarding the plane crash caused by a Russian missile.