In a statement, the coalition said the deal is "designed to minimize civilian casualties" and that the convoy of evacuation buses would be searched and screened by a U.S.-backed ground force. But it also tried to distance itself from the arrangement brokered by a local civilian council and Arab tribal elders.
"We do not condone any arrangement that allows Daesh terrorists to escape Raqqah without facing justice, only to resurface somewhere else," said Brig. Gen. Jonathan Braga, using an Arabic acronym for the Islamic State. "We remain concerned about the thousands of civilians in Raqqah who remain subject to Daesh cruelty."
Three years after Raqqa became the de facto capital of a self-proclaimed caliphate spanning Syria and Iraq, the Islamic State is now clinging onto its last foothold there.
The battle for the city began in June, with a U.S.-backed militia known as the Syrian Democratic Forces leading heavy street-by-street fighting amid intense coalition airstrikes and shelling.
In comments to the Associated Press, Omar Alloush, an official from Raqqa's local council, confirmed said that local fighters have been included in the evacuation agreement. The apparent exclusion of foreign fighters, who stand the least chance of slipping away unnoticed, suggested that they would now be left alone to defend their final sliver of territory.
It was unclear Saturday whether the evacuation buses would leave for SDF-controlled territory or for that still held by the Islamic State. In September, U.S. warplanes temporarily blocked a convoy carrying hundreds of the group's fighters and their families after Hezbollah and the Syrian government permitted them to withdraw from a besieged enclave on the Lebanon-Syria border.
On Saturday, Col. Ryan Dillon, a spokesman for the U.S.-led coalition, said it was now important that the actions of those evacuated were "monitored and tracked" and that Syrian militants were not able to reenter the conflict.
Hundreds of fighters in Raqqa are believed to have surrendered in recent days, leaving a bombed-out ghost city in their wake. But thousands of civilians remain trapped in the middle of the remaining dogfight, acting as human shields for the Islamic State's militants and forcing the SDF to slow its final advance.
U.S.-led coalition airstrikes in the province have also killed hundreds of civilians, according to monitoring groups and a war crimes inquiry by the United Nations.
Raqqa's strategic significance has diminished as a range of international forces rolled back Islamic State territory across Syria and Iraq, with senior leaders moving east to the border regions between the two.
But the loss of the city would mark a symbolic blow. During more than three years of control, the city's name became synonymous with the Islamic State's most brutal excesses. Footage showing beheadings and the severing of limbs as punishment were shown around the world. Attacks on European soil were planned there, too.
On Saturday, the Syrian Defense Ministry said it had captured the eastern city of al-Mayadeen, a key Islamic State holdout where Western officials believe the group's top officials have moved in recent months.
The pro-Syrian government Al-Ikhbariya TV quoted an unnamed military official as saying that the militant group's defenses in Mayadeen collapsed on Saturday, with troops chasing the remaining Islamic State fighters out of town as engineers cleared land mines. Video footage from the area showed military vehicles rolling through empty streets, with soldiers flashing victory signs for the camera.
Suzan Haidamous in Beirut and Zakaria Zakaria in Istanbul contributed to this report.