GENEVA (Reuters) - A renewed assault on Islamic State fighters in the Iraqi city of Mosul could force 250,000 civilians to flee, if they can find a way out, the U.N. refugee agency UNHCR said on Friday.

Displaced families who fled from fighting with Islamic State militants arrive at Hashid Shaabi, or Popular Mobilization Forces, camp west of Mosul, Iraq. REUTERS/Stringer

Such an exodus would be on top of roughly 162,000 people already displaced by Iraqi government efforts to retake the city since October. Such numbers, although high, remain well below UNHCR’s initial contingency plans, which anticipated a million people or more fleeing from the city.

“As many as 250,000 Iraqis could be displaced from their homes with the anticipated escalation of conflict in densely-populated western Mosul,” UNHCR spokesman Matthew Saltmarsh said.

An expected intensification of fighting around Hawija, 130 km southeast of Mosul, could displace another 114,000, adding to the 82,000 who have fled since August, risking ambushes and death.

In Iraq’s biggest military operation since the fall of Saddam Hussein in 2003, government forces have seized most of east Mosul. But they have yet to cross the Tigris river, leaving the western half in the hands of the jihadists, who declared a caliphate there two-and-a-half years ago.

U.N. Special Representative for Iraq Jan Kubis told the U.N. Security Council on Thursday that retaking western Mosul would be a massive challenge, with complex urban operations.

“There is no question that civilians will be at extreme risk when the fighting starts in the western sections of Mosul,” he said.

“Humanitarian partners are bracing for a variety of possible scenarios in the western sections, including a possible mass exodus, prolonged siege-like conditions, or a sequenced and managed evacuation by the Iraqi Security Forces.”

He praised Iraqi forces, including the Popular Mobilisation Forces, for prioritizing the protection of civilians after learning from mistakes in previous battles to wrest control of cities from IS.

“I however express my concern over disturbing reports of looting and destruction of civilian property, and looting of humanitarian aid by armed groups operating in support of the Iraqi Security Forces, in particular by some local resistance groups.”

Hundreds of civilians allegedly disappeared in a previous battle, for the city of Fallujah, and the Iraqi authorities have still not published heir findings into what happened there, he said.