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.

Russian President Vladimir Putin apologized for the “tragic incident,” which left 38 people dead, though he stopped short of taking responsibility.

Flight J2-8243 crashed on Wednesday in a ball of fire near the city of Aktau in Kazakhstan after diverting from southern Russia, where Ukrainian drones were reported to be attacking several cities. At least 38 people were killed in the crash while 29 survived.

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.