SINJAR, Iraq — Kurdish Iraqi fighters, backed by U.S.-led airstrikes, launched a major assault today aiming to retake the strategic town of Sinjar, which the Islamic State group overran last year in an onslaught that caused the flight of tens of thousands of Yazidis and first prompted the United States to launch the air campaign against the militants.

Hours into the operation, the Kurdish Regional Security Council said forces were in control of a section of Highway 47, of one of IS’s most active supply lines.

The advance completely isolates members of the IS group in Sinjar from militant strongholds in Syria and northern Iraq.

Some 7,500 peshmerga fighters were closing in on Sinjar from three fronts, the security council said in a statement. In addition to taking the town and the highway, Operation Free Sinjar aimed to establish “a significant buffer zone to protect the city and its inhabitants from incoming artillery.”

Heavy gunfire broke out early today as peshmerga fighters began their approach amid aerial bombardment. An Associated Press team saw a small American unit at the top of a hill along the front line, calling in and confirming airstrikes.

The coalition said 24 airstrikes were carried out over the past day, striking nine militant tactical units, nine staging areas and destroying 27 fighting positions, among other targets. Coalition aircraft have conducted more than 250 airstrikes over the past month.