BEIRUT — The U.S.-led coalition battling the Islamic State group said Wednesday that it won’t accept a negotiated withdrawal for hundreds of IS militants holed up in the Syrian city of Raqqa, once the extremists’ de facto capital.

The remarks by coalition spokesman Col. Ryan Dillon came as coalition allies were working out ways to safely evacuate an estimated 4,000 civilians who remain trapped in the city.

The coalition has said IS militants are holding some civilians as human shields, preventing them from escaping as the fight enters its final stages for the last remaining slice of Raqqa in militant hands. The city, on the banks of the Euphrates River, has been badly damaged by the fighting, and activists have reported that over 1,000 civilians have been killed there since June.

The United Nations estimates 8,000 people are trapped in Raqqa, and has called on all parties to the conflict to take all measures to protect civilians. The U.N. said September was the worst month in 2017 for civilians in Syria.

Dillon said the Raqqa Civil Council, a local administration of Arab and Kurdish officials, was leading the discussions to ensure safe evacuation of civilians as the fight for Raqqa enters its final stages. However, it was not clear with whom the council is speaking inside Raqqa. A Kurdish-led force, the Syrian Democratic Forces, is leading the U.S.-backed battles on the ground.

Dillon said discussions about the fate of the militants remaining in the city have focused on “unconditional surrender.”

A negotiated withdrawal “is absolutely something that we as a coalition would not be a part of or agree with,” Dillon said. Between 300 and 400 militants are believed to be holed up in about 1.5 square miles of Raqqa, including in the city’s stadium and a hospital, he said.

The militants are believed to be using the stadium as a weapons warehouse and prison, and the hospital as a headquarters.