PENTAGON - U.S.-led coalition airstrikes against Islamic State targets in Iraq and Syria killed about 2,500 militants in December, a military spokesman said Wednesday.

Colonel Steve Warren also told reporters that the terror group had lost more than 20,000 square kilometers of land it once controlled in Iraq and about 2,000 square kilometers of land in Syria.

Iraq and Syria: ISIL's Reduced Operating Areas a
Iraq and Syria: ISIL’s Reduced Operating Areas as of April 2015

"We believe ISIL is now in a defensive crouch," he said, using an acronym for Islamic State. "If you're part of ISIL, we will kill you. That's our rule."

Intensified coalition airstrikes have decreased IS oil production from 45,000 barrels per day to 34,000, he said, making IS oil revenue drop 30 percent.

Last week, Iraqi troops backed by U.S.-led airstrikes and Sunni tribesmen pushed IS out of the Iraq city of Ramadi, the capital of sprawling Anbar province.

Warren said Iraqi forces clearing Ramadi discovered civilians who had been killed "execution-style" and others who had been used as human shields by IS. He said hundreds of civilians, including children, were now getting help from Iraqi forces.

The extremist group still controls tens of thousands of square kilometers of land, including the major cities of Mosul, Iraq, and Raqqa, Syria.

The jihadists have also managed to hold on to a very important strip near the Turkish border, where they can smuggle goods and fighters into the territory IS holds.

“You take ISIL away from that border, it is a truly self-contained entity and a very different problem,” Brett McGurk, the special presidential envoy for the Global Coalition to Counter Islamic State, told reporters Tuesday.

The chairman of the Joint Chiefs of Staff, General Joe Dunford, is visiting Turkey this week to discuss the war against Islamic State. Vice President Joe Biden will visit Turkey later this month.

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