washington u.s. vice president joe biden visit serbia kosovo next week white house say tuesday white house statement announce aug. 15-17 balkan tour say biden would hold meet country president prime minister say subject would discuss unite state last month transfer two inmates u.s. military prison guantanamo bay cuba serbia u.s. secretary state john kerry thank serbia call significant humanitarian gesture kerry visit serbia kosovo december stop kosovo underscore western concern slow pace progress 16 years u.s.-led nato air war set former serbian province road independence kosovo mainly muslim secular staunchly pro-american country declare independence 2008. u.s. vice president biden visit serbia kosovo next week