Iraqi government forces have launched an offensive to liberate the western part of the city of Mosul from the so-called Islamic State.
Hundreds of military vehicles, backed by air power, rolled across the desert towards the jihadists’ positions early on Sunday.
Iraqi forces retook two villages south of the city in the first hours of the operation, a top commander said.
The offensive was formally announced by Iraqi Prime Minister Haider al-Abadi.
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.
The UN has voiced concern about civilians trapped there, 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.
Lieutenant General Stephen Townsend, the commander of the US-led coalition forces, said in a statement on Sunday: “Mosul would be a tough fight for any army in the world.”
Ahead of the launch of the operation, Mr Abadi said in a televised speech: “We announce the start of a new phase in the operation, we are coming to Nineveh to liberate the western side of Mosul.”
“Our forces are beginning the liberation of the citizens from the terror of Daesh [IS],” he added, quoted by AFP news agency.
Iraqi forces have now all but surrounded the western part of Mosul, while the US-led coalition has been carrying out air strikes on IS targets.
Winning the city back has never been just about the military objective of driving IS out of its stronghold, the BBC’s Sebastian Usher says.
Minimising civilian casualties and avoiding reprisals will be key to regaining the trust of the city’s population in the Iraqi state itself, he adds.