One should differentiate these from sub-camps of Nazi concentration camps operated by the SS, which were also called Arbeitskommando. Because of the two different types there is some confusion in the literature, with the result of occasional reports of prisoners-of-war being held in concentration camps. In some cases the two types were physically adjacent, when both POWs and KL-inmates were working at a large facility such as a coal mine or chemical plant.[2] They were always kept apart from each other.