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.

Moscow, RussiaRussian President Vladimir Putin apologized to Azerbaijan’s leader on Saturday, following the deadly crash of an Azerbaijan Airlines plane in Kazakhstan, according to a statement from the Kremlin.

T hursday is an official day of mourning in Azerbaijan as an investigation is underway to determine what caused an airplane carrying 67 passengers to crash on Christmas Day in Kazakhstan, killing 38 and leaving at least 29 survivors. Video posted by CNN shows the plane crash-landing, exploding into a fireball and plumes of black smoke.

Authorities in Kazakhstan are investigating the cause of an Azerbaijan Airlines plane crash in the country, which killed 38 people and injured 29 others on Christmas Day.The big picture: Flight J2-8243 was diverted while en route from Baku,

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.

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.