Over the past 72 hours, US and coalition aircraft conducted 46 bombing raids in support of Kurdish peshmerga troops near Mosul and 80 hours of reconnaissance flights, the military said in a statement.
Kurdish officials said previously that they cut a key road that links Mosul with Tal Afar to the west.
The US military's statement confirmed that "forces from the Iraqi Kurdistan Region seized ground formerly held by the enemy, including a critical road junction that ISIL was using to resupply their stronghold in Mosul."
The statement also said that coalition air power and other assistance in recent days meant that Kurdish forces "now hold the gains they have made and are postured to retake additional territory from ISIL in vicinity of Mosul."
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US and Iraqi commanders have vowed to recapture the large stretch of territory seized by the IS group last year and Mosul is seen as a pivotal battleground in any future counter-offensive.
General Lloyd Austin, head of US Central Command, told the Wall Street Journal on Thursday that Iraqi troops should be ready to launch an operation to try and retake Mosul by the summer.
After nearly 2,000 air strikes against IS extremists in Iraq and Syria since August, the IS group still holds virtually all of the ground it captured last year, including much of western Anbar province.
But US commanders say the air war has halted the IS group's momentum, killed thousands of its fighters and put it on the defensive.
The head of "Operation Inherent Resolve," Lieutenant General James Terry, said this week's Kurdish operation "is another superb example" of how the IS group can be defeated using "well-led ground forces" assisted and advised by the US-led coalition.
The military's statement was issued by Terry's command which is based in Kuwait.