I am extremely concerned for 1.5 million people living in Mosul: Stephen O'Brien

The UN deputy Secretary General for Humanitarian Affairs and Emergency Relief voiced grave concern for 1.5 million people living in Mosul as operations to retake the Iraqi city of Mosul began.

"I am extremely concerned for the safety of up to 1.5 million people living in Mosul who may be impacted by military operations to retake the city from ISIL," Stephen O'Brien said, referring to the Islamic State jihadist group.

He warned that "families are at extreme risk of being caught in cross-fire or targeted by snipers." The northern city was where IS leader Abu Bakral-Baghdadi publicly proclaimed a "caliphate" straddling Iraqand Syria in June 2014.

With the support of Iran and a US-led coalition, Iraqi forces have since regained much of the ground lost to IS.Mosul is the extremist group's last major strong hold in Iraq.

Iraqi Prime Minister Haider al-Abadi has said only government forces will enter Mosul, a Sunni-majority city thatIS seized with relative ease partly amid local resentmenttowards the Shiite-dominated security forces.

"Depending on the intensity and scope of the fighting, as many as one million people may be forced to flee their homes in a worst-case scenario," O'Brien said in a UN statementobn Sunday. Indeed, children and elderly are among those at greatest risk, he said.

"Tens of thousands of Iraqi girls, boys, women and menmay be under siege or held as human shields. Thousands may be forcibly expelled or trapped between the fighting lines,"O'Brien added. US Secretary of Defence Ash Carter said the operation waskey to defeating the jihadist group. "This is a decisive moment in the campaign to deliver ISIL a lasting defeat," Carter said in a statement. "We are confident our Iraqi partners will prevail againstour common enemy and free Mosul and the rest of Iraq fromISIL's hatred and brutality."