National Security Advisor Susan Rice said U.S.-led coalition forces have recaptured nearly 55 percent of areas in Iraq which were previously held by the Islamic State group, also called ISIS. Rice added she believes Iraq’s Mosul and Syria’s Raqqa will soon be liberated from ISIS control as well.

“The Iraqi Security Forces inside of Iraq have taken back about 55 percent of the populated territory that ISIL originally seized back in 2014,” Rice told CNN’s Fareed Zakaria on Sunday, using another acronym for the militant group. “They have now, with our support and that of our 68-country coalition, encircled Mosul and they're beginning to move into parts of Mosul.”

In spite of the significant progress, Rice admitted that clearing the militant group from Iraq and Syria completely would still be “a very difficult fight.”

“ISIL has been entrenched there for several years now. It built up very significant defenses. And so we can’t expect that to be quick and easy. But I believe that in due time that [effort] will succeed, and we are working very assiduously to support the Iraqi Security Forces [ISF] as they do that,” she said.

Susan Rice National Security Advisor Susan Rice heads to her seat before a ceremony awarding the Presidential Medal of Freedom to various recipients in the East Room of the White House in Washington, D.C., Nov. 22, 2016. Photo: REUTERS/CARLOS BARRIA

Rice added the offensive in Raqqa, the group’s Syrian headquarters, would be quite a challenge given the city’s predominantly Sunni Arab population. ISIS fighters are also Sunni Muslims.

“This is a complicated endeavor because the force that is best capable of conducting the isolation consists not only of Syrian Arabs, but also of Syrian Kurds. And Raqqa will need to be ultimately taken by Syrian Arabs, who would be more accepted by the population,” she said.

The United Kingdom’s senior-most commander in Iraq and Syria said Monday daily attacks by coalition forces against the terrorist group in Iraq led to “an extraordinary amount of progress.” However, Major General Rupert Jones warned that ISIS was still defending Mosul vigorously.

“What we have all got to then have is patience and what you want is the ISF to clear their way through the city in a deliberate manner,” Jones reportedly said. “They could hard charge their way through the city and there would be an awful lot of civilian casualties but it has been really impressive to watch [Iraqi Prime Minister Haider al-] Abadi downwards really care about civilian casualties. Therefore, they are taking a deliberate manner and trying to minimize their own casualties.”