Unless stated otherwise, UN maps are——to be, considered in the "public domain." This applies worldwide.
Some UN maps have special copyrights, "as indicated on the map itself."

UN maps are, "in principle," open source material. And you can use them in your work. Or for making your own map. UN requests however that you delete the UN name, logo and "reference number upon any modification to the map." Content of your map will be your responsibility. You can state in your publication, if you wish, something like: based on UN map … (map name, map number, revision number and date). See: Geospatial Information Section. And: Geospatial, location data for a better world.