HAMAM AL-ALIL, Iraq -- U.S.-backed Iraqi forces launched a large-scale military operation on Sunday to dislodge Islamic State militants from the western half of Mosul city, a battle that is expected to be prolonged and difficult due to a densely packed civilian population and older, narrower streets. Separately, the army's 9th Division moved into the village of Bakhira, also southwest of the city, the Iraqi Ministry of Defense said.The United Nations meanwhile warned that hundreds of thousands of civilians trapped inside their houses "are at extreme risk," with dwindling fuel and food supplies and scare drinking water and electricity. Story highlights Iraqi forces claim 79 ISIS militants killed on first day of operation

Mosul's west bank has been one of the Iraqi force's toughest challenges

(CNN) Iraq has launched an operation to regain control of western Mosul from ISIS militants, Prime Minister Haider al-Abadi said Sunday. 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 told Reuters on Saturday. "Three out of five people now depend on untreated water from wells for cooking and drinking as water systems and treatment plants have been damaged by fighting or run out of chlorine," said Peter Hawkins, of the U.N. agency for children.The humanitarian agencies were gearing up to aid 250,000 to 400,000 civilians who may flee due to fighting, the statement said. According to estimates, between 750,000 and 800,000 civilians reside in the western section of Mosul. 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."
Iraq Prime Minister Haider al-Abadi says U.S.-backed Iraqi forces have launched an operation to regain control of western Mosul from ISIL militants. The United Nations says humanitarian agencies are setting up in these older sections of the city where, already, food and fuel supplies are dwindling, running water is scarce, and electricity in many neighborhoods is unreliable for the estimated 800,000 civilians.