Tactical nuke - not strategic ...
The blast radius of a small tactical nuke is several city blocks ...
W70 variable yield warhead ranges between 1 and 100 kilotons of TNT.
The lowest selectable yield of a tactical B61 (Mod 3 and Mod 4) is 0.3 kilotons. http://nuclearweaponarchive.org/Usa/Weapons/B61.html
But, here - choose your weapon, pick your target location and check the effects for yourself (have a blast, LOL)
http://www.nuclearsecrecy.com/nukemap/
Thanks
Nuke affect
Using a Pakistani warhead - on loan - of 45 KT produces an estimated fatalities: 4,790 with an estimated injuries: 5,220 when detonated at 0 feet on Puerto de Anapra - most non-ISIS casualties would come from the loss of the U of El Passo.
Using 3 re-manufactured Davy Crocketts with a yeild of 20 KT saturating the area of Puerto de Anapra and the Rancho Anapra non-ISIS estimated fatalities: 0 estimated injuries: 340.
That would seem to be the best option for a no notice strike, plus they could be arty launched - saving wear and tear on the troops.