Kurdish Iraqi fighters, backed by U.S. airstrikes, launched an assault Thursday aimed at retaking the strategic town of Sinjar. ISIS had seized Sinjar last year murdering, raping, and enslaving thousands of Yazidis.

According to Reuters, the Kurds have captured three villages and penetrated parts of Highway 47, a supply route between Raqqa in Syria and the Iraqi city of Mosul, both of them Islamic State base areas.

“The ground assault began in the early morning hours of Nov. 12, when peshmerga units successfully established blocking positions along Highway 47 and began clearing Sinjar,” said the coalition in a statement.

Some 7,500 Kurdish fighters were deployed on a three-pronged front seeking to reclaim Sinjar, Kurdish authorities said.

Another spokesman, Col. Steve Warren, told the Reuters news agency that some U.S. advisers were among the peshmerga ground forces to help with targeting airstrikes. He gave no further details. The Associated Press reported that a small American military team was seen on a hilltop, directing and confirming airstrikes

The Washington Post reported that the capture of Sinjar by Islamic State militants in August 2014 sent tens of thousands of Yazidis fleeing to Mount Sinjar, where they became trapped. Thousands of women were captured by the group and have been used as sex slaves.

Should the Kurds win a victory in Sinjar it may give government forces and Shiite militias the biggest push to increase efforts to defeat the Islamic State. ISIS still controls large areas of Iraq and Syria.