Pushing the Islamic State (ISIS/ISIL) out of its de facto capital of Raqqa, Syria, may take months, predicted a commander of the U.S.-backed Syrian Kurdish forces fighting against the jihadists, according to Reuters.

“It could take another three to four months to finish Raqqa,” Haval Gabar, a 25-year-old commander of the Kurdish People’s Protection Units (YPG) militia, which is leading the U.S.-backed Syrian Democratic Forces (SDF), an Arab-Kurdish alliance, told Reuters.

Although the SDF has been steadily advancing against ISIS, Gabar acknowledged, “They’ve [jihadists] laid many mines, that’s one of the biggest difficulties. As for car bombs, they don’t use them every day, but if our forces are advancing down a street, then they deploy them.”

The YPG commander’s comments came after U.S.-allied troops, primarily the Kurdish-dominated alliance known as the Syrian Democratic Forces (SDF), surrounded ISIS in central Raqqa.

“We’ve cleared about half of Old Raqqa … and we’re advancing on all axes,” declared Gabar.

The YPG-led SDF force, backed by U.S. airstrikes and coalition special forces, is directing the offensive to liberate Raqqa from ISIS.

“We’ll be done soon,” an unidentified YPG fighter told Reuters. “We kill 10 to 15 Daesh a day.”

The YPG is the armed wing of the Kurdish Democratic Union Party (PYD) that controls large swathes of northern Syria.

SDF fighters reportedly encircled the ISIS terrorists in central Raqqa earlier this week.

Citing fighters in Gabar’s unit and other SDF militias, Reuters notes that the fight for Raqqa is expected to get tougher, adding that jihadists from the Russian region of Chechnya are particularly deadly.

Gabar, the Kurdish commander, estimates that there are no more than 1,000 ISIS-linked jihadists left in Raqqa, believed to be the group’s largest stronghold in Syria.

The chief noted that several hundred terrorists had already surrendered.

“Maybe 600 Daesh have surrendered. It’s mostly foreign fighters left in the city now. Those with families tend to be the ones to hand themselves over,” he told Reuters.

The U.S.-backed SDF has been trying to liberate Raqqa from ISIS for months. An Iraqi campaign, backed by the United States, already cleared ISIS out of Mosul, the group’s former largest stronghold in Iraq.

In 2014 ISIS declared Raqqa, the capital of its so-called “caliphate” that extended into Iraq. According to the U.S. government, ISIS has lost more than 80 percent of the territory it held at its peak around the beginning of 2015