US-backed Iraqi forces have begun moving towards Mosul airport, the first target of a ground offensive to capture the western side of the city that remains under control of Islamic State.
Iraqi Prime Minister Haider al-Abadi earlier on Sunday announced the formal start of a ground offensive on western Mosul, asking the Iraqi forces to ''respect human rights'' during the battle.
IS militants are essentially under siege in western Mosul, along with an estimated 650,000 civilians, after US-backed forces surrounding the city forced them from the east in the first phase of an offensive that concluded last month.
Iraqi federal police units are leading a northward charge on the Mosul districts west of the Tigris River, aiming to capture the Mosul airport, according to statements from the armed forces joint command.
They captured several villages and a local power distribution station in the first hours and killed several militants including snipers, the statements said.
"Mosul would be a tough fight for any army in the world," the commander of the US-led coalitions forces, Lieutenant General Stephen Townsend said.
Iraqi planes dropped millions of leaflets in western Mosul warning residents the battle to dislodge IS was imminent as troops began moving in their direction, the Iraqi Defence Ministry said on Saturday.
Up to 400,000 civilians could be displaced by the offensive as residents of western Mosul suffer food and fuel shortages and markets are closed, United Nations Humanitarian Coordinator for Iraq Lise Grande said.
Commanders expect the battle to be more difficult than in the east because tanks and armoured vehicles cannot pass through its narrow streets and alleyways.
The militants have also developed a network of passages and tunnels that will enable them to hide and fight among civilians, disappear after hit-and-run operations and track government troop movements.
Western Mosul contains the old city centre, with its ancient souks, Grand Mosque and government buildings.
It was from the pulpit of the Mosul Grand Mosque that IS leader Abu Bakr al-Baghdadi declared a "caliphate" over parts of Syria and Iraq in 2014.
