BAGHDAD — Upcoming military offensives in Iraq against ISIS, including an assault on the northern city of Mosul, could displace at least 2.3 million people, the United Nations humanitarian coordinator for Iraq said on Thursday.

The prediction of such a vast humanitarian emergency creates additional complications for the Iraqi government and its U.S. allies, who have announced plans for offensives to drive ISIS fighters this year from most of their Iraqi territory.

More than 3.4 million people across Iraq have already been forced by conflict to leave their homes, according to the United Nations. In the past month, 85,000 people fled Fallujah, amid a military campaign that has recaptured large parts of the city.

Most of the displaced are from Iraq’s minority Sunni community, raising concerns among officials that U.S.-backed military gains against ISIS will not bring stability to Iraq more than 13 years after a U.S.-led invasion toppled Saddam Hussein.

ISIS militants have lost ground in recent weeks to a number of enemies on several fronts in Iraq and Syria, with the main battles still looming for the caliphate’s two de facto capitals, Mosul and Raqqa.

In Mosul, by far the largest city under the militants’ control, the worst case scenario could see one million people displaced, said Lise Grande, the U.N. humanitarian coordinator for Iraq