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.

Azeri President Ilham Aliyev says Vladimir Putin’s apology isn’t enough, in a confrontation that shows Moscow’s waning influence over former Soviet territories.

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 extraction of flight data from the Brazilian-made Azerbaijan Airlines plane that crashed in Kazakhstan last month was completed at a lab run by Brazil's air force, according to a statement released by the entity on Monday.