It will take 40 to 50 years to clear the mines, improvised explosive devices and other unexploded ordnance from Iraq and Syria, the United Nations said.
"We are looking at decades of work for these countries to look like post-World War II Europe where we still find some unexploded ordnance here and there," Agnes Marcaillou, director of the United Nations Mine Action Service, told a news conference marking International Mine Awareness Day.
She said her office, which also deals with IEDs and unexploded ordnance, is looking at a "ballpark figure" of between $170 million to $180 million a year to clean up the areas retaken from the so-called Islamic State extremist group in Iraq.
Marcaillou said that figure includes $50 million annually needed just to rid weaponry from Mosul.
Iraqi forces and a U.S.-led international coalition have been engaged in a months-long operation to retake Mosul from ISIS.