"We don't believe that Baghdad is under imminent threat," spokesman Rear Admiral John Kirby told a news conference.
He acknowledged several deadly car bombings in Baghdad, including one claimed by the IS group, but said the city was not on the verge of collapsing.
"It's not the first time in recent weeks or even months that there's been IED attacks inside Baghdad," he said, using the military's abbreviation for an improvised explosive device or home-made bomb.
"There are not masses of formations of ISIL forces outside of Baghdad about to come in," he said.
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Iraqi security forces "continue to stiffen their defensive positions in and around the capital, and in a very competent, capable way."
Kirby said "terrible" weather and sand storms in recent days had hampered US-led air strikes Iraq, where IS fighters have gained ground in Anbar province, west of Baghdad.
"It's made it very hard for us to get intelligence surveillance and reconnaissance platforms up over to see what we're trying to do in Iraq," he added.