Reports say Iraqi government forces have launched an offensive to liberate the western part of the city of Mosul from the Islamic state militants.
Hundreds of military vehicles, backed by air power, rolled across the desert towards (IS) positions early on Sunday.
Iraqi forces retook several villages south of the city in the first hours of the operation, taking them within striking distance of the Mosul Airport.
Fears have been voiced about the safety of many thousands of trapped civilians.
Meanwhile, leaflets warning residents of an imminent offensive were earlier dropped over the west of the city.
The UN has therefore voiced concerns about civilians trapped in Mosul amid reports that they could number up to 650,000.