More than 300,000 people have fled Mosul since the start of the U.S.-backed campaign to dislodge Islamic State from the northern Iraqi city in October, the United Nations said on Tuesday.

The United Nations’ International Organisation for Migration estimates the number of people currently displaced to be 302,400, the office of the U.N. Humanitarian Coordinator in Iraq said in a statement.

Iraqi forces, backed by a U.S.-led coalition, have taken most districts of Mosul, Islamic State’s last major stronghold in Iraq and the city where the group’s leader, Abu Bakr al-Baghdadi, declared a caliphate nearly three years ago.

They are now battling to take the northwestern part from Islamic State but the civilian death toll has mounted in the densely populated Old City, where the militants are dug in amongst residents.

More people are expected to flee the fighting and camps for the displaced north and east of Mosul are expanding, the U.N. statement said.