State-sanctioned Shiite militias have launched an attack on the Islamic State group west of the Iraqi city of Mosul but reiterated that they would not enter the Sunni majority city.

Jaafar al-Husseini, a spokesman for the Hezbollah Brigades, said they launched an offensive Saturday along with other militias toward the town of Tel Afar, which had a Shiite majority before it fell to IS in 2014. He says Iranian forces are advising the fighters and Iraqi aircraft are providing airstrikes.

Iraq launched a massive operation to retake militant-held Mosul, its second largest city, last week. The involvement of the Shiite militias has raised concerns the battle could aggravate sectarian divisions.

Al-Husseini says the militias will focus on Tel Afar and on securing the western border with Syria.