Macedonia now only admitting refugees from warzones * Migrants transferred to Athens must leave Greece * Twelve more migrants drown off Greek island (Adds official statement, updates figures) By Alexandros Avramidis IDOMENI, Greece, Dec 9 (Reuters) - Greek police rounded up some 2,300 migrants who had been stranded for three weeks at the border with Macedonia and transported them to Athens on Wednesday, dashing their hopes of seeking asylum in northern Europe. Scuffles broke out but not on the scale of recent clashes between police and the migrants, who are mostly from Pakistan, Morocco, Algeria and Somalia.