Sounds like war. An atrocity would have been simply firebombing it from the air, and dropping anti-personnel munitions on all the fleeing refugees. This way, you remove the enemy, and risk no lives of your own forces. Probably cheaper, too.
The very act of sending in ground forces rather than simply wiping out the city is a humanitarian...to say nothing of actually giving warning and letting everyone who wanted to leave! And then offering at least some reparations afterwards for property damage. (which, in a combat zone, is obviously going to be extreme).
It was an entrenched enemy. Fortified. Not sure how you'd go about killing them. But killing them was the goal. Ya know. Because war is focused violence.
Maybe we could have asked nicely?