As the seat of government, the city houses the federal ministries and a number of other federal institutions, including the National Bank. It is also the headquarters of the Universal Postal Union, one of the specialised agencies of the United Nations. In addition it is the seat of public services, such as Swiss Post (the state-owned post office) and the Swiss Federal Railways. The city has a small airport in the suburb of Belp. Although Zurich is Switzerland's main rail hub, Bern has a direct rail service to several of the major cities of Switzerland, as well as to European cities such as Paris, Berlin, Barcelona and Milan.