MOUNT SINJAR, Iraq — With coalition warplanes circling overhead, Kurdish fighters pushed into the contested northern Iraqi town of Sinjar on Sunday, touching off heavy clashes with Islamic State militants who have controlled the area for months. The battle for Sinjar and the surrounding areas has become the latest focus in the campaign to take back territory lost to the Islamic State group during the militants’ summer blitz that captured much of northern and western Iraq. Loud explosions and intense gunbattles could be heard echoing from inside the town as U.S.-led coalition warplanes bombed Islamic State militants from the sky. The spokesman for the Kurdish forces, Jabbar Yawar, said the fighters were still facing resistance from pockets of Islamic State militants still inside the town and that it is “far from cleared.”