The U.N. envoy for Iraq says 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.

Jan Kubis told the Security Council on Wednesday that efforts by the Iraqi Security Forces, the Peshmerga and other allies are making steady progress liberating the city, while trying to minimize civilian casualties.

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

And he warned that reconciliation at the community and national level was necessary if the victories against IS are to be lasting.