Hitting future ISIS targets will be much more complicated

(CNN) – If the U.S. decides to increase the number of targets across Iraq, it will face ground difficulties of taking on ISIS.

It's one thing to take out ISIS militants around Amerli, a farming hamlet of less than 20,000 people in the middle of nowhere, where U.S. airstrikes are extremely effective.

It's a different ball game in the strongholds like Mosul, Tikrit, and Fallujah where there are millions of people. It would fundamentally become an urban warfare.

CNN's Anna Coren reports.