BELGRADE, Serbia — Serbia's Parliament speaker on Sunday officially called for a national referendum this month on a new constitution that would declare U.N.-run Kosovo is part of Serbia regardless of ongoing negotiations on the breakaway province's future. Predrag Markovic set the plebiscite for Oct. 28-29, urging voters to come out in large numbers and support the new constitution, which underscores Serbia's opposition to possible independence for Kosovo. Independence, sought by the ethnic Albanian majority in Kosovo, is one of the options under discussion in U.N.-brokered talks. In Kosovo, a separatist leader dismissed Serbia's move as a "provocation." Kosovo's Deputy...