Updated at 11:40 a.m. ETThe U.S.-backed Syrian Democratic Forces are in the process of kicking ISIS out of Raqqa, the extremist group's self-declared capital where it has terrorized civilians and plotted attacks against targets linked to the U.S. and its allies. Now ISIS fighters are reportedly bottled up in a stadium complex in the Syrian city.As of Tuesday afternoon local time, the SDF controlled "more than 90 percent" of Raqqa, according to U.S. Army Col. Ryan Dillon, spokesman for Operation Inherent Resolve.The gains have left ISIS "on the verge of a devastating defeat," Dillon said in an update shortly before noon ET. In the past few days, he said, "about 350 fighters" have surrendered.Celebrations began to break out among the SDF in Raqqa on Tuesday, as the end of a four-month offensive seemed near. But Dillon tells NPR's Ruth Sherlock that fighting could continue as ISIS fighters hold out in booby-trapped buildings.Rigged explosives present a peril of their own. The commander of the Raqqa Internal Security Forces — who was to help secure the city after ISIS was defeated there — died Monday, Dillon said, "when he was walking through Raqqa and triggered an IED, and he had two of his colleagues that were with him."The near-total takeover of Raqqa is being marked three years after the Operation Inherent Resolve task force was officially established by the Department of Defense.The task force says it has liberated "over 6.6 million Iraqi and Syrian from Daesh control" and taken back nearly 94,000 square kilometers of land — nearly 90 percent of the territory seized by the extremist group in 2014.As for how many fighters ISIS currently has at its disposal, the task force said its estimates range from 3,000 to 7,000 who are continuing to fight in Iraq and Syria. The group also says it has degraded ISIS' ability to fund its operations, by shutting down 90 percent of its oil revenues.The Raqqa landmarks that have been wrested from ISIS' control, Dillon notes, include the Al-Naim traffic circle, once used by the militants to carry out executions and acts of depraved violence.The precise number of ISIS fighters who remain at large in the city isn't known. Over the weekend, word emerged that at least 100 ISIS fighters had surrendered. From Monday into Tuesday, the militants were isolated in two areas: a hospital and at the municipal stadium, according to the Syrian Observatory for Human Rights. The stadium had been used as a prison.After fighters at the hospital reportedly surrendered, that left the stadium — and the Observatory says that when negotiations for more surrenders became drawn out, the SDF launched an assault Tuesday backed by U.S. special forces.Made up of Arab and Kurdish fighters, the SDF began a push to take Raqqa in early June. They were backed by airstrikes from the U.S.-led coalition — strikes targeting ISIS that have been blamed for causing civilian deaths.From Beirut, Ruth reports: