http://www.treas.gov/ofac/ccigars.pdf

"Only persons returning from Cuba after a licensed visit there are permitted to bring Cuban cigars into the United States provided the value of such cigars does not exceed 100 US dollars, and that the cigars are for that person's personal use and not for resale...it is illegal for travelers to bring into the United States Cuban cigars acquired in third countries (such as Canada, England, or Mexico)."