Iraqi government forces have resumed their push towards western Mosul, the last major stronghold of so-called Islamic State (IS) in Iraq.
Artillery fire could be heard in the distance, reports the BBC's Quentin Sommerville, who is embedded with government troops.
Launching the operation on Sunday, the army seized several villages.
The eastern part of the city was liberated from IS last month after heavy fighting.
Concern has been voiced by the UN about the welfare of civilians trapped in Mosul, amid reports that they could number up to 650,000.
Leaflets warning residents of an imminent offensive were earlier dropped over the west of the city.
Military officials say the western side of the city, with its narrow, winding streets, may prove a bigger challenge than the east.
All bridges from there to the west of the city, across the Tigris river, were destroyed.
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