The fighters of Islamic State rode in on four tanks and 10 cars, each mounted with a heavy machine gun. They opened fire as they stormed down the road to Tall Ghazal, about eight miles south of the Turkish border. Outgunned by the jihadist onslaught—as they had been since it began on Sept. 19—the Kurdish defenders fell back, took cover behind outlying buildings, and waited for an opportunity to counterattack.

"We ambushed them when they approached," says Ferhat, a member of the People's Protection Units (known by its Kurdish initials, YPG), the militia defending the besieged, isolated canton of Kobane, in Syria's north. In the firefight that ensued, the Kurds destroyed three Islamic State vehicles. The jihadists retreated into a neighboring village, leaving some of the Kurds dead or injured. A sniper's bullet struck Ferhat in the leg, shattering his tibia. Ferried to safety by friends, he recounted his battlefield experience from Turkey, his left leg held together by metal pins, the pillow on which it rested caked in dried blood.

Ferhat spoke to Bloomberg Businessweek and two other reporters on condition that his identity and his current location not be disclosed. The YPG is an offshoot of the Kurdistan Workers' Party, or PKK, which Turkey, the U.S., and the European Union consider a terrorist group. His account could not be independently verified, though it is consistent with other reports from the frontlines.

As a fighting force, says Ferhat, Islamic State militants are as ruthless as they are effective. They shell villages from afar, then advance, guns blazing, pressing forward with recently captured tanks, Humvees, and pickup trucks, before sending in fighters on foot. They have no mercy on the locals. "In one village, I saw 17 bodies with no heads," says Ferhat. "One of them was a child, one was a woman, and the rest were men."

Occasionally, the extremists exhibit reckless if not crazy behavior. Says Ferhat, "One of their guys charged straight at us waving a large knife. We shot him dead." Ferhat puts such incidents down to possible drug use. "When we capture them, we sometimes find syringes in their bags," he says. Some of the dead had what he described as "capsules" or "vials" in their mouths.

Many Islamic State fighters in Kobane appear to come from abroad. Those captured or killed, says Ferhat, are regularly found carrying IDs from countries like Egypt, Tunisia, Belgium, Turkey, and Italy.

The fighting has been desperate on the Kurdish side. One badly wounded Kurdish fighter, Ferhat recalls, "blew himself up" to avoid being captured alive by the jihadists. Another ran up to one of Islamic State's tanks, threw open the hatch, and tossed in an explosive, killing everyone inside, including himself.

An economics student at college before the war, Ferhat joined the YPG more than two years ago. He found himself stationed in and around Kobane, facing off against a succession of foes, from the Free Syrian Army (FSA) to the Nusra Front and now Islamic State. The FSA, which initially accused the Kurds of siding with the regime of Syrian President Bashar al-Assad, has since allied itself with the YPG against the jihadists.

Ferhat has been told he won't be able to walk for another two months. As soon as he gets better, he insists, he will return to Syria and defend Kobane. By then, there may not be much left to defend. On Wednesday, the jihadists captured Tall Ghazal, where Ferhat had been wounded. On Friday, they appeared to have tightened their stranglehold over Kobane. In some places, the fighting had come so close to the Turkish border that locals and journalists could monitor developments with binoculars. On Friday, at least two shells fell on Turkish soil.

Ferhat remains defiant. Islamic State captured Mosul, he says, because the locals, including the Iraqi forces, either lacked morale or supported the new occupiers. That will not be the case with the Kurds of Kobane, he says. "To take it, they'll have to kill all of us."