AMMAN- Islamic State militants on Saturday pushed back US-backed forces trying to advance into their stronghold of Manbij for the first time since a major offensive to capture the city and cut off the militant's main strategic access route to Turkey, a monitoring group and Kurdish sources said.The Syria Democratic Forces (SDF), comprised of Kurdish and Arab fighters and backed by the air power of a US-led coalition to fight Islamic State and aided by US special forces, have been involved in the month-long Manbij operation aimed to seal off their last stretch of Syrian-Turkish frontier.The British-based Syrian Observatory for Human Rights confirmed the militants had evicted SDF troops from a main district south of the city which has been the scene of heavy fighting after suicide bombers blew up an explosive laden car.The militants also recaptured a village northwest of the city.