The U.S.-led coalition in Syria confirmed Friday that the Islamic State's self-described capital city of Raqqa has been fully liberated, congratulating partner forces on the victory.

Lt. Gen. Paul Funk, commanding general of the Combined Joint Task Force, called the achievement a "hard-won victory by local Syrian fighters for the world" following four years of occupation by the terrorist group, which had seen the city as the center of its global caliphate.

"Today, however, Raqqa is free. The ISIS caliphate has crumbled. Their capital is lost," Funk said in a video statement.

The fight for Raqqa, carried out by the U.S.-backed Syrian Democratic Forces, began in June after a wider three-year fight started by former President Barack Obama had already liberated vast expanses of northern Iraq from ISIS including the city of Mosul.

The Trump administration and Defense Secretary Jim Mattis have ramped up operations and employed new tactics aimed at surrounding and eliminating ISIS fighters.

Funk said that those operations were continuing along the Euphrates River valley in both Syria and Iraq where the group still has holdouts.

The Pentagon said earlier this week that ISIS still has about 6,500 fighters in the region and Funk warned about "deadly combat" to come.