"There was an offensive action by the enemy in the vicinity of Mosul dam, a combination of US air strikes and Iraqi forces were able to repel that," spokesman Colonel Steven Warren told reporters.
US and coalition warplanes conducted 12 bombing raids on Tuesday and Wednesday against the IS group near Mosul dam, destroying a large IS unit, a mortar position, three vehicles and other targets, US Central Command said.
The IS militants briefly held Mosul dam in August but Kurdish forces and Iraqi army troops -- backed up by US air strikes -- succeeded in retaking the dam later that month.
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The large dam in northern Iraq is a crucial piece of infrastructure and IS has repeatedly tried to seize it back.
The dam is the country's largest and if destroyed or dismantled, it could unleash major flooding of the city of Mosul and the capital Baghdad.
US Central Command also said US aircraft renewed air raids on the IS group near Kobane in northern Syria, with six strikes near the border town over the past 24 hours.
Kurdish forces, backed by US air power, have been holding out against an IS offensive around Kobane for weeks.