Iraqi government forces have seized several villages as they move towards an assault on the last area held by the so-called Islamic State (IS) in Mosul.
Hundreds of military vehicles, backed by air power, rolled across the desert towards IS positions early on Sunday.
The progress on Sunday in the south of the city, the second biggest in Iraq, takes them within striking distance of Mosul airport.
Fears have been voiced about the safety of many thousands of trapped civilians.
The offensive was formally announced by Iraqi Prime Minister Haider al-Abadi early on Sunday.
Army Staff Lieutenant General Abdulamir Yarallah said in a statement that elite Rapid Response units captured the villages of Athbah and Al-Lazzagah – two villages south of Mosul airport.
Government forces retook the eastern side of the city, the last major IS stronghold in Iraq, last month. But military officials say the western side, with its narrow, winding streets, may prove a bigger challenge.
For now, there is no advance from eastern Mosul as all bridges from there to the west of the city, across the Tigris river, have been destroyed.