BAGHDAD: Iranian-backed Iraqi Shi'ite paramilitary groups are about to launch an offensive on Islamic State positions west of Mosul, assisting in the military campaign to take back the city, a spokesman said on Friday.

The operation will target an area close to Turkey and where a sizeable ethnic Turkmen population lives, likely causing alarm in Ankara.

The militias, collectively known as Hashid Shaabi or Popular Mobilization Forces, have completed preparations to move in the direction of Tal Afar, a stronghold of Islamic State west of Mosul, from their positions in Qayyara, south of the city.

"A few days or hours separate us from the launch of operations there,” spokesman Ahmed al-Asadi told state TV.

The population of Tal Afar, about 55 km (35 miles) west of Mosul, was mix of Sunni and Shi'ite ethnic Turkmens until Shi'ites fled the town after Islamic State's ultra-hardline Sunni militants took over the region in 2014, declaring a caliphate over parts of Iraq and neighbouring Syria.

Turkey's Foreign Minister Mevlut Cavusoglu said on Wednesday his country, which has troops deployed north of Mosul inside Iraqi territory, will take measures if there is an attack on Tal Afar.

Turkey fears the use of Shi'ite militias in the US-backed offensive on Mosul will lead to sectarian strife in the mainly Sunni region and cause an exodus of refugees.

Earlier announcements by the PMF that they will be involved in the offensive on Mosul, Islamic State's last major stronghold in Iraq, triggered warnings from human rights groups of sectarian violence in the mainly Sunni province.

Shi'ites make up a majority in Iraq but Sunnis are predominant in the north and the west.

The PMF officially reports to the Shi'ite-led government of Prime Minister Haider al-Abadi who announced on Oct. 17 the start of the offensive on Mosul, Iraq's second-largest city, with the backing of a U.S-led coalition.

The PMF was formed in 2014 to help push back Islamic State's sweeping advance through the northern and western provinces.

Amnesty International says that in previous campaigns, the Shi'ite militias have committed ``serious human rights violations, including war crimes'' against civilians fleeing Islamic State-held territory.

The UN in July said it had a list of more than 640 Sunni Muslim men and boys reportedly abducted by a Shi’ite militia in Falluja, a former militant stronghold west of Baghdad, and about 50 others who were summarily executed or tortured to death.

The government and the PMF say a limited number of violations had occurred and were investigated, but they deny abuses were widespread and systematic.