As relations between East and West began to sour with the coming of the Cold War, it had become the victim of the hostilities. Although services continued operating through all occupation sectors, checkpoints were constructed on the borders with East Berlin and on-board "customs checks" were carried out on trains. From 1958 onward, some S-Bahn trains ran non-stop through the western sectors from stations in East Berlin to stations on outlying sections in East Germany so as to avoid the need for such controls. East German government employees were then forbidden to use the S-Bahn since it travelled through West Berlin.