<Ul> <Li> Oscar Niemeyer </Li> <Li> Le Corbusier </Li> <Li> Harrison & Abramovitz </Li> </Ul> <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>

Is the head quarter of uno in usa