<Li> Harrison & Abramovitz </Li> <Tr> <Th> Main contractor </Th> <Td> Fuller, Turner, Slattery, and Walsh </Td> </Tr> <P> The United Nations is headquartered in New York City, in a complex designed by Brazilian architect Oscar Niemeyer and built by the architectural firm Harrison & Abramovitz . The complex has served as the official headquarters of the United Nations since its completion in 1952 . It is located in the Turtle Bay neighborhood of Manhattan, on 17 to 18 acres (6.9 to 7.3 ha) of grounds overlooking the East River . Its borders are First Avenue on the west, East 42nd Street to the south, East 48th Street on the north and the East River to the east . The term "Turtle Bay" is occasionally used as a metonym for the UN headquarters or for the United Nations as a whole . </P> <P> The United Nations has three additional, subsidiary, regional headquarters, or headquarters districts . These were opened in Geneva (Switzerland) in 1946, Vienna (Austria) in 1980, and Nairobi (Kenya) in 1996 . These adjunct offices help represent UN interests, facilitate diplomatic activities, and enjoy certain extraterritorial privileges, but only the main headquarters in New York City contains the seats of the principal organs of the UN, including the General Assembly and Security Council . </P>

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