The offensive to retake the northern city of Mosul from Islamic State miliants continues. The head of the U.S. military’s Central Command said small groups of ISIL fighters are gradually trickling out of the city after suffering heavy casualties.

Some terrorists dumped their weapons and wore plain clothes to look like civilians, which has made it harder for coalition drones and planes to track them. Special forces are still at least six kilometers east of the city and have faced mortar and machine gun fire, as well as suicide truck bombs.

The United Nations has said that Iraq will likely face the worst humanitarian crisis in history, with more than 1 million people affected by the battle in Mosul. The U.N. also predicts around 200,000 residents will flee their homes in the coming weeks.