The top U.S. commander in Iraq says Iraqi Security Forces now have Mosul "firmly under their control," and has issued formal congratulations to both Iraqi and Kurdish forces on their "hard-fought victory."

"Make no mistake; this victory alone does not eliminate ISIS and there is still a tough fight ahead," Lt. Gen. Stephen Townsend said in statement. "But the loss of one of its twin capitals and a jewel of their so-called caliphate is a decisive blow."

The statement issued by the U.S.-led coalition said while there are still areas of the Old City of Mosul that must cleared of explosive devices and possible ISIS fighters in hiding, the ISF has recaptured Mosul.

"The global Coalition fighting ISIS congratulates Prime Minister [Haider] al-Abadi and the Iraqi Security Forces on their historic victory against a brutal and evil enemy," Townsend said.

Mosul, Iraq's second largest city, was overrun by ISIS in 2014, and Iraqi forces launched the operation to retake Mosul last October.

The U.S. military statement noted that ISIS left much of the city in ruins.

"During its occupation of Mosul, ISIS destroyed many of the city's religious and cultural treasures, including the al-Nuri Mosque and the Tomb of the Prophet Jonah. It terrorized and brutally murdered thousands of civilians, including scores of women and children. ISIS used mosques, schools and hospitals as bomb-building facilities and fighting positions; but in the end, ISIS was still defeated."