The conduct of any activities, or the acquisition of any benefits (as defined in
section 4301(a)(1) of this title), outside the United Nations Headquarters District by any individual employed by, or authorized by the United Nations to conduct official business in connection with, that organization or its agencies, or by any person or agency acting on behalf thereof, may be permitted or denied or subject to reasonable regulation, as determined to be in the best interests of the United States and pursuant to this chapter.