Security expert Margaret Gilmore has explained that coalition forces have a '"long and bloody" battle on their hands in their attempt to re-take the ISIS-held city of Fallujah in Iraq.
Supported by US air strikes, Iraqi special forces have this week launched a ground assault to the east of the city, facing stiff resistance from the terrorist group.
The city has been under ISIS control since January 2014.
A victory for the coalition is viewed as crucial, with a liberated Fallujah serving as a staging point to recapture the city of Mosul, another key stronghold for the group.
But Gilmore, who serves as a security associate for the Royal United Services Institute (RUSI), outlined why re-taking Fallujah will be no easy task.
"The fighters hide amongst the civilian population, so it's difficult to get them out because we don't bomb civilians," she told Julia Hartley-Brewer.
"ISIS don't hold themselves in barracks and don't have a clear frontline.
"They fight from house to house and will try to draw in Iraqi fighters to suit their advantages.
"Plus, they've built a network of tunnels so they can escape when the Iraqi army gets close.
"It's pretty dire at the moment."
The broadcaster explained why ISIS will fight particularly fiercely to maintain their hold over Fallujah.
"The symbolic significance is [Fallujah] is the first big city ISIS took two years ago," she said. "It's also very close to Baghdad. They are using the position to launch attacks on the nearby villages.
"This advance has to be stopped."
While Gilmore emphasised the difficulty faced by the coalition, she told Julia that the militant group is also struggling.
"It could take an awfully long time" she said. "On the other hand, there are issues over food, water, electricity... it will be more and more difficult for ISIS to sustain themselves.
"The final battle will have to be done by troops on the ground. It's essential the Iraqis win this, but I have no doubt it will be long and bloody."