The operation to liberate the Iraqi city of Mosul marks the beginning of the end of the Islamic State group's so-called caliphate in Iraq, the UN envoy to the country told the United Nations Security Council on Wednesday.

Jan Kubis said efforts by the Iraqi security forces, the peshmerga and other allies are making steady progress in liberating the city, while seeking to minimize civilian casualties.

Kubis also said he has received credible reports of IS forcing tens of thousands of civilians to relocate inside Mosul, for use as human shields.