The United Nations has warned of the possibility that millions of people could be displaced, as Iraqi forces launch a military campaign on retaking Mosul from ISIL militants.

The U.N. released figures earlier this week showing that 200,000 people are expected to be displaced in the first several weeks. As many as 1.55 million people may be impacted by the military campaign.

Chaloka Beyani, the U.N. Special Rapporteur on the human rights of Internally Displaced Persons, warned that a total of 1 million people could be displaced. He added that 700,000 people in Mosul could also be in need of emergency shelter, following the intensification of fighting.

Some 5,000 to 6,000 Iraqis have reportedly fled the city and taken shelter at the border with Syria. More than 3,000 are still waiting to cross the border.