"We've said all along that there are going to be ebbs and flows. This is a difficult, complex, bloody fight," Pentagon spokesman Colonel Steven Warren told reporters.
"And there's going to be victories and setbacks. And this is a setback," Warren told reporters.
Citing reports of atrocities by the jihadists in Ramadi, Warren said civilians living in the city now faced the IS group's "trademark brutality."
"We will retake it in the same way we are slowly but surely retaking other parts of Iraq, and that is with Iraqi ground forces combined with coalition air power."
A senior officer in the US military command overseeing the anti-IS war effort in Iraq and Syria last week insisted the jihadists remained "on the defensive," even as the Iraqi army's defenses were crumbling in Ramadi.
But Warren acknowledged that the IS extremists now had control over Ramadi.
The IS group "is obviously not on the defensive in Ramadi.
