I think its possible that they could exist depending on the reason they people where being held and who was being held.
I think the idea of slave labor is much more likely though as jester mentioned all ready. In fact I suspect a lot of well established communities would have slave labor.
I think the U.S. could establish camps fairly easily, due to the fact that they have several "mock ups" of concentration camps and "training areas" that actually already exist! like the one at Redding ton naval airbase here in Maine where the USN conducts is cold weather training and sere school. I have seen it and thought it could be used for nefarious purposes instead of "training" it is extremely remote most people don't even know its there.
here is something to get your conspiratorial juices flowing:
http://www.fourwinds10.com/siterun_d...p?q=1214512721
while the above information may be wrong or grossly misrepresented (for instance the German ww2 camp listed in Maine called Camp Houlton is now the site of the Houltan airport.) But its basically t2k information thats already made up for you! Why not use it?
Brother in Arms