Iraq's Shia militias announced on Monday that they will participate in the next major battle against the militant Islamic State (IS) group after the Iraqi forces' victory in Mosul last month.

The Shia militias did not fight in the urban part of Mosul, Iraq's second-largest city, but were key in clearing far-flung villages of IS and capturing supply lines in the desert west of Mosul toward Iraq's border with Syria.

The spokesman for the government-sanctioned umbrella — known as the Popular Mobilization Forces (PMF) and mostly made up of Shia fighters — says the participation of the militiamen is “essential” in the upcoming fight for the town of Tal Afar, west of Mosul.

About 150 kilometres east of the Syrian border, Tal Afar was once home to both Shia and Sunni ethnic Turkmen.

“Today we want to speak loud and clear that (the PMF) are actively involved in Tal Afar military operations and will participate in all areas where operations are taking place,” PMF spokesperson Ahmed al-Asadi told reporters in Baghdad.

In past fights against IS in Iraq, including the battles for the cities of Tikrit and Fallujah, the Shia militias were accused of sectarian killings and other abuses against minority Sunnis. They acknowledge some abuses may have occurred but claim that those responsible have been disciplined.

Monday's announcement may increase tensions between Iraq and neighbouring Turkey.

Turkish Prime Minister Binali Yildirim has repeatedly warned that military operations in and around Mosul should not lead to any demographic changes on the ground, reflecting concerns that once territory is liberated from IS, Iraqi Kurdish or Shia forces may push out Sunni Arabs or ethnic Turkmen.