The United Nations has expressed 'grave concerns' over reports that the so-called Islamic State are using civilians as human shields in Mosul.

UN Human Rights chief Zeid Ra Al Hussein called for the protection of civilians to be at the forefront of military planning as the Iraqi Government and allied forces attempt to re-take Iraq's second city.

"We are gravely concerned by reports that ISIL [IS] is using the civilians in and around Mosul as human shields as the Iraqi forces advance.

"They are keeping civilians close to their offices or places where fighters are located, which may result in civilian casualties," said Ravina Shamdasani, Spokesperson for the Office of the High Commissioner for Human Rights (OHCHR).

"We have verified information that there were several instances since the 17 October where ISIL [IS] has forced people to leave their homes in outline villages to head to Mosul" she added.

The Human Rights spokesperson added they had received reports that members of the terrorist group have shot dead civilians who have tried to rise up against them or who they suspect have been disloyal.

Among the reports received by OHCHR is that so-called IS has forced hundreds of families out of surrounding areas of the city and pushed them towards Mosul.

The Human Right organisation is also examining reports that at least 40 civilians were shot dead by IS in one of the villages outside Mosul.

The Office of the High Commissioner for Human Rights is urging the Iraqi authorities to take all possible steps to prevent armed groups operating alongside the Iraqi Security Forces from any form of revenge attack on civilians fleeing Mosul.