It is not clear what exactly the weapon system being used is or who owns it, but I would guess that it is the BM21 "Grad" ("Hail") truck mounted multiple rocket launcher system filling sky with almost certain death.

These rockets may not be "smart" but they are extremely effective over dozens of miles at "suppressing" large areas that may be filled with enemy formations or material. The sheer speed at which these rockets fly and the volume of fire that can be deployed in a short amount of time causes the BM21, and other indirect fire mobile rocket systems like it, to be highly feared by opposing ground units, especially ones that are operating in hilly or mountainous terrain.

You can read more about this deadly weapon system here.