If those are "only" prisoners, then it should be okay to let foreign inspectors in and talk to the "prisoners", shouldn't it?
https://www.reuters.com/article/us-rights-un-usa-torture-idU...
https://news.un.org/en/story/2020/05/1063292
https://www.thedailybeast.com/why-the-us-wont-let-the-un-loo...
https://www.tasnimnews.com/en/news/2015/07/25/809496/united-...