British Army: Get as much 1st hand intel as possible, flood the streets with men, talk to the locals, clear out every building (with soldiers), conduct regular patrols, both on foot and armour, set up road blocks to hinder militia movement.
In short, prevent it from ever really blowing up into a full scale conflict by stopping the militia moving and getting supplies, making it too difficult to operate for the enemy.
Best peacekeepers in the world, but would probably make for a boring mission (unless you end up in a bayonet fight like in Iraq)