Kurdish forces in northern Syria pushed back an advance by Islamic State fighters toward a strategic town on the Turkish border Thursday and appealed for U.S.-led airstrikes to target the insurgents' tanks and heavy armaments.

Islamic State launched a new offensive to try to capture the border town of Kobani more than a week ago, besieging it from three sides. At least 140,000 Kurds have fled the town and surrounding villages since Friday, crossing into Turkey.

Kurdish and Islamic State fighters exchanged artillery and machine-gun fire in a cluster of villages about 15 km west of Kobani, where the frontline appeared not to have moved significantly for several days, a witness said.