Major cities? This simply means that the bassiji will function as a formal political internal control as well as the nominally religious function they presently possess. They won't be there for defense against foreign forces, they'll be there to stifle internal dissent.
As well they might, because should the people they've been oppressing decide they've had enough there will be bassiji swinging from the lamposts.
For more on this........
Police state: Iran grants sweeping new powers to Basij militia goons