The NDAA did give such permission,however, since removed, supposedly. Do some checking, there are multiple sources on NDAA Section 1021 or the original line, Section 1031 on the indefinite detention of Americans or legal residents in the USA. (Link is to Wikipedia, so, who knows?)
This is a scary proposition if it is still a possibility. I can remember the arguments, one side saying take it out, the other saying even though it says American citizens in one place there is another which says Americans are exempt, so, you tell me, does it apply?
(CNN)If President-elect Donald Trump decides to make good on his campaign pledge to “load up” the prison camp in Guantanamo Bay, Cuba, with new domestic terror suspects caught in the US — including American citizens — legal experts say he is asking for an unprecedented constitutional […]