BEIRUT — Vacations cut short, hurried goodbyes and last-minute flights at exorbitant fares — residents and tourists, heeding warnings of an impending war, are scrambling to leave summertime Lebanon as tensions build between Israel and Hezbollah, Iran’s Lebanese ally.

       Britain has ordered its citizens to “leave Lebanon now,” while Paris is urging French nationals to depart “as soon as possible.” The U.S. Embassy in Beirut, in an alert over the weekend, instructed Americans who wish to leave to “book any ticket available to them.”