U.S.-backed forces have advanced roughly 5 kilometers, or 3.1 miles, in the northern Syrian city of Raqqa over the past week, pushing back Islamic State militants in a grueling offensive to seize the terrorist group's last significant stronghold.

Army Col. Ryan Dillon, a spokesman for the U.S.-led coalition battling ISIS, told the Washington Free Beacon that although Syrian Democratic Forces now control 55 percent of the city, the military expects difficult fighting ahead.

Dillon said at a Pentagon briefing earlier this month that SDF troops were steadily closing in on ISIS fighters, but acknowledged progress had slowed from the first two weeks of the operation when the Kurdish-led forces achieved rapid territorial gains.

In the 11 weeks since the SDF began the offensive to retake Raqqa, ISIS has taken advantage of the closely spaced buildings and tight streets of the city to plant large IEDs in an attempt to stave off coalition advances.

Dillon said the 1,500 ISIS militants estimated to remain in Raqqa are paralleling many of the same tactics used in the Iraqi city of Mosul, such as booby-trapping civilian homes and hiding suicide bombers among civilians and SDF troops. Jihadists are also using human shields, including women and children, to prevent American airstrikes from targeting key structures.

Dillon previously told the Free Beacon the U.S. military had seen video of ISIS militants ordering young kids to stand outside of several known factories around Raqqa used to manufacture vehicle-borne improvised explosive devices.

Though the strategies have slowed the offensive against ISIS, SDF troops are still making crucial gains.

Dillon told the Associated Press on Friday the SDF had linked up their eastern and western fronts in southern Raqqa, joining forces to encircle ISIS fighters. He said the advance demonstrates the steady progress SDF troops are achieving despite the stiff resistance from ISIS.