US-backed Syrian forces declare victory over ISIS in its former 'capital,' Raqqa ISIS took control of Raqqa in 2014..

 -- U.S.-backed Syrian forces declared victory over ISIS in the terror group's former de facto capital of Raqqa.

“We proudly announce today from the heart of the city of Raqqa the victory of our forces in the major battle to defeat the ISIS terror organization, which we defeated in the capital of its alleged caliphate," the Syrian Democratic Forces said in a statement in Arabic on Friday.

Raqqa, nestled on the northern bank of the Euphrates River in Syria, fell into the hands of ISIS militants in 2014 and became the heart of their self-declared Islamic caliphate.

Friday's proclaimed victory comes after weeks of fighting between ISIS and the Syrian Democratic Forces, an alliance of Kurdish and Arab militias backed by the United States, with entire neighborhoods of the backwater city now in ruin.

The U.S.-led coalition fighting ISIS also issued a statement Friday that congratulated the Syrian force on its victory in Raqqa. The coalition called the liberation of Raqqa and an earlier victory over ISIS in Mosul, Iraq, in July, "turning points for the terrorist organization whose leaders grow ever more distant from a dwindling number of terrorist adherents."

However, U.S. Army Lt. Gen. Paul E. Funk II, commanding general of the Combined Joint Task Force-Operation Inherent Resolve, cautioned that "a tough fight still lies ahead."

"The military defeat of Daesh is essential, but not sufficient," Funk said, using the Arabic acronym for ISIS. "We are still fighting the remnants of Daesh in Iraq and Syria, and will continue to facilitate humanitarian efforts assisting citizens adversely affected by a brutal occupation, who face a long battle to gain their freedom."

The destruction in Raqqa adds to the wider damage from the Syrian civil war that is now in its seventh year. Half of Syria's population is displaced either within the country's borders or abroad. Meanwhile, more than 5 million Syrians lack access to basic supplies and services, according to the International Committee of the Red Cross.

ABC News' Lena Masri and Elizabeth McLaughlin contributed to this report.