UPDATE: An Iranian reader emails:
The word “supporters” is in this context a little misleading. Those are not “supporters” of the regime, or of Khamenei, that carry out killings, shootings and terrorizing of the populace at large. They are the regime’s paid agents. They are the security apparatus. The trucks seen in the video linked to, belong to the security forces and not “supporters” as the word is ordinarily understood.
I apologize for sounding pedantic, but I felt the term, as used, gave a false impression as to exactly who was doing the killing in Iran.