Kurdish forces drove Islamic State militants back from the oil-rich city of Kirkuk in northern Iraq on Monday, in an advance backed by heavy airstrikes from a U.S.-led coalition.

Speaking to a local television channel near the frontline, Kirkuk Gov. Najmaldin Karim, who was wearing a helmet, said the purpose of the offensive was to secure Kirkuk, which the Kurds have held since last summer.

Kurdish fighters retook around 100 sq. km (40 sq. miles), including about a dozen villages, from Islamic State to the south and west of Kirkuk, killing some 100 militants, a statement from the region's security council said.