Cuba isn't happy about Guantanamo
Cuba has criticised the US's treatment of prisoners in Guantanamo, calling the facility a "concentration camp". This is a bit rich coming from a regime which incarcerates dissidents and has little regard for due process, but on the other hand if even they think something is bad then it must be pretty terrible.
If Cuba really wants to support the human rights of those in Guantanamo, though, it has a very clear course of action open to it: allow lawyers for those imprisoned to petition Cuban courts for a writ of Habeus Corpus. The US government's chief argument for denying detainees access to American courts is that Guantanamo is not under US jurisdiction. The Cubans should call their bluff, and watch them squirm.