Turkish President Recep Tayyip Erdogan on Saturday warned Shiite militias in Iraq against attacking Turkmen residents of Tal Afar, a town near the Islamic State group's Mosul bastion.

"If the Hashed al-Shaabi sow terror there, then our response will be different," Erdogan said, in comments carried by the state-run Anadolu news agency, without specifying what measures would be taken.

The Hashed al-Shaabi, a paramilitary umbrella organisation dominated by Iran-backed Shiite militias, launched an operation on Saturday to cut Islamic State-held Mosul off from Syria.

They began pushing toward Tal Afar from the western approach to the city, the only side where ground forces, who have advanced from the north, east and south, are not yet deployed.

Tal Afar was a Shiite-majority town of mostly ethnic Turkmen before Sunni IS extremists overran it in 2014, and its recapture is a main goal of Shiite militia fighters.

The town is also key to IS for linking its Syrian stronghold of Raqa to Mosul, currently the target of a massive military offensive launched by the Iraqi government.

Erdogan assured that Turkey "would not look favourably" on an attack by Shiite militias on Tal Afar.

Since the offensive against Mosul began, Turkey has stated its opposition to the participation of Shiite militias.

The militias have in the past been accused of committing atrocities when entering Sunni-majority towns. They have already said they have no plans to enter Mosul.

Erdogan's veiled warning came two day after his foreign minister, Mevlut Cavusoglu, said that Turkey would view an advance on Tal Afar as a threat and was ready to take "adequate measures".

Hundreds of Turkish soldiers are based at the Bashiqa camp in Mosul province in northern Iraq, officially to train Sunni volunteers.