The six-month-old operation to retake the Iraqi city of Mosul from the Islamic State group has forced around half a million people to flee their homes, the United Nations said Monday.
Iraqi forces began the country's biggest military operation in years exactly six months ago and recaptured the east side of the city in January.
But an assault launched the following month on the part of Mosul that lies west of the Tigris river has seen a sharp rise in displacement.
"The sheer volume of civilians still fleeing Mosul city is staggering," Lise Grande, the UN's humanitarian coordinator in Iraq, said in a statement.
"Our worst case scenario when the fighting started was that up to one million civilians may flee Mosul. Already, more than 493,000 people have left, leaving almost everything behind," she said.
Iraqi forces have been making significant gains in west Mosul over the past two months but the toughest battles could yet lie ahead, with die-hard jihadists hunkering down in the treacherous streets of the Old City.
The UN estimated that another half million civilians were still in IS-controlled areas of west Mosul.
"Mosul has pushed us to our operational limits," said Grande.
UN chief Antonio Guterres said on March 31 during a visit to a displacement camp near Mosul that the aid effort was woefully underfunded and called for greater international solidarity.