It's thought Islamic State fighters in the city of Mosul will try to flee Iraq, if the city is seized.

Iraqi troops, with air support from coalition partners, are locked into the battle to reclaim the IS stronghold.

Fellow of foreign policy at the Brookings Institute Michael O'Hanlon told Rachel Smalley it'll be hard for the fighters to blend in with the civilians.

"You'd have to get out and go somewhere else, either within Iraq, or Syria."

However, he said it's "not that easy to move either, and certainly not in large numbers all at once, because of course, we control the air."

There are concerns about the impact the battle of Mosul will have on civilians.

It's thought a million civilians will be caught up in the fighting and try to flee the city.

Head of World Vision's Syrian Crisis Chris Weeks said they're particularly concerned about the impact the fighting will have on children.

"It's going to be noisy, it's going to be confusing, it's going to be frightening, and I imagine fleeing the city to unknown places after that is going to be even more frightening."