BEIRUT/RAQQA, Syria: Daesh's (ISIS) defeat in its Syrian bastion of Raqqa was a "historic" achievement, the U.S.-backed force that led the battle said during an official ceremony in the city Friday.

The Kurdish-led Syrian Democratic Forces (SDF) retook full control of Raqqa on Tuesday, in what spokesman Talal Sello said was a "historic victory" that he dedicated to "all humanity."

Raqqa and surrounding province will be part of a decentralized federal Syria, the SDF also said Friday.

"We pledge to protect the borders of the province against all external threats, and we confirm that the future of Raqqa province will be determined by its people within the framework of a decentralised, federal democratic Syria in which the people of the province will run their own affairs," the SDF said in a statement.