美国有线新闻 CNN 伊拉克拉响收复摩苏尔之战 或将重创ISIS（在线收听）

First story centers on a battle that's begun in the Middle Eastern nation of Iraq. You've heard us talk a lot about the ISIS terrorist group. ISIS is an acronym for Islamic State in Iraq and Syria, and that's what they've been trying to create.

But right now, ISIS is fighting to hold on to the Iraqi city of Mosul, which they took over in 2014. And if ISIS loses Mosul, it could signal the beginning of the end for ISIS in Iraq.

The battle started early Monday morning. Iraq's military says it inflicted heavy losses of life and equipment on ISIS in an area southeast of the city. Iraqi troops are leading a coalition of other groups in trying to push ISIS out. Hundreds of U.S. troops are also involved, though the Pentagon says they're not on the front line. And the forces that are can call in air support when they meet with tough resistance from the terrorist.

One terrorism expert says the major challenge of this battle will be avoiding hurting Mosul's civilians while overpowering ISIS's defenses.

They've had months to prepare for this. But international officials say there's no doubt the fight is an important one.

CLARISSA WARD, CNN SENIOR INTERNATIONAL CORRESPONDENT: The battle for Mosul is a really big deal, and here's why.

SUBTITLE: Why Mosul matters.

WARD: Mosul is the second biggest city in Iraq and it's the last remaining ISIS stronghold in the country. It's also the place where ISIS leader Abu Bakr al-Baghdadi first declared that he had established an Islamic caliphate or state.

Now, the last time the Iraqi army was in Mosul was back in 2014, ones were fleeing from ISIS fighters. This time, it's hoping to reverse those losses.

Iraqi army forces won't be the only ones on the battlefield, though. Kurdish, Peshmerga forces will be involved and the U.S. military will also be playing a supportive role.

But the battle won't be easy. Officials estimate there are between three and five thousand ISIS fighters still inside the city and they have created an elaborate network of defenses. They fill moats with oil and set it alight, creating these thick black plumes of choking smoke. Houses are booby trapped, the streets are littered with IEDS.

And then there's the human toll. An estimated 1 million civilians are still leaving in the city of Mosul and the U.N. says that the exodus that could follow a battle might be one of the biggest manmade displacements in recent times.

Some commanders estimate it could take as much as three months to take the city, and then there's the aftermath to deal with. But if the operation is successful, it will deal a major blow to ISIS.