The United States Embassy in Athens on Friday warned of the risk of violent attacks against visitors “perceived to be foreign migrants” after a rise in racially motivated assaults in Greece, where far-right sentiment is on the rise. In a message on its Web site, the embassy noted that American citizens of African, Asian, Hispanic or Middle Eastern descent were most at risk. The warning follows an increase in violent attacks against immigrants living in Greece and foreign visitors, mostly by members or supporters of Golden Dawn, a neo-Nazi political party.