A senior United Nations official says the fight against the Islamic State group has left behind massive destruction in Iraq and enormous planning and investment are needed for rebuilding.

Assistant Secretary-General and Deputy Executive Director of UN-Habitat, Aisa Kirabo Kacyira tells The Associated Press on Tuesday that the level of destruction in liberated areas "is really, really huge." Kacyira is visiting Iraq to evaluate the destruction.

After a fierce, nearly three-year fight with the extremist group, which once controlled swath area in northern and western Iraq, U.S.-backed Iraqi forces succeeded in driving out the militants from nearly all the areas — but at a high cost. Thousands were left dead, entire neighborhoods in ruins and more then 3 million displaced from their homes.